Re: shared-memory based stats collector

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От Kyotaro HORIGUCHI
Тема Re: shared-memory based stats collector
Дата
Msg-id 20190221.160555.191280262.horiguchi.kyotaro@lab.ntt.co.jp
обсуждение исходный текст
Ответ на Re: shared-memory based stats collector  (Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>)
Ответы Re: shared-memory based stats collector  (Arthur Zakirov <a.zakirov@postgrespro.ru>)
Список pgsql-hackers
Hello.

At Wed, 20 Feb 2019 15:45:17 +0900 (Tokyo Standard Time), Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp> wrote in
<20190220.154517.24528798.horiguchi.kyotaro@lab.ntt.co.jp>
> At Fri, 15 Feb 2019 15:53:28 -0300, Alvaro Herrera <alvherre@2ndquadrant.com> wrote in
<20190215185328.GA29663@alvherre.pgsql>
> > Talk about moving the whole file to another subdir ...
> 
> Sounds reasonable. It was a searate patch at the first but
> currently melded to bloat the patch. I'm going to revert the
> separation/moving.

Done. This verison 16 looks as if the moving and splitting were
not happen. Major changes are:

 - Restored old pgstats_* names. This largily shrinks the patch
   size to less than a half lines of v15.  More than that, it
   gets easier to examine differences. (checkpointer.c and
   bgwriter.c have a bit stale comments but it is an issue for
   later.)

 - Removed "oneshot" feature at all. This simplifies pgstat API
   and let this patch far less simple.

 - Moved StatsLock to LWTRANCHE_STATS, which is not necessary to
   be in the main tranche.

 - Fixed several bugs revealed by the shrinked size of the patch.

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center
From 5e52ba57f3708c3411fff836473e8c1a572d063e Mon Sep 17 00:00:00 2001
From: Kyotaro Horiguchi <horiguchi.kyotaro@lab.ntt.co.jp>
Date: Fri, 29 Jun 2018 16:41:04 +0900
Subject: [PATCH 1/6] sequential scan for dshash

Add sequential scan feature to dshash.
---
 src/backend/lib/dshash.c | 188 ++++++++++++++++++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h |  23 +++++-
 2 files changed, 206 insertions(+), 5 deletions(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index f095196fb6..1e8c22f94f 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -112,6 +112,7 @@ struct dshash_table
     size_t        size_log2;        /* log2(number of buckets) */
     bool        find_locked;    /* Is any partition lock held by 'find'? */
     bool        find_exclusively_locked;    /* ... exclusively? */
+    bool        seqscan_running;/* now under sequential scan */
 };
 
 /* Given a pointer to an item, find the entry (user data) it holds. */
@@ -127,6 +128,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)                    \
     (size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)        \
+    (((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)        \
     (((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +158,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)    \
     ((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)                \
+    ((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)                                \
     (hash_table->buckets[                                                \
@@ -228,6 +237,7 @@ dshash_create(dsa_area *area, const dshash_parameters *params, void *arg)
 
     hash_table->find_locked = false;
     hash_table->find_exclusively_locked = false;
+    hash_table->seqscan_running = false;
 
     /*
      * Set up the initial array of buckets.  Our initial size is the same as
@@ -279,6 +289,7 @@ dshash_attach(dsa_area *area, const dshash_parameters *params,
     hash_table->control = dsa_get_address(area, control);
     hash_table->find_locked = false;
     hash_table->find_exclusively_locked = false;
+    hash_table->seqscan_running = false;
     Assert(hash_table->control->magic == DSHASH_MAGIC);
 
     /*
@@ -324,7 +335,7 @@ dshash_destroy(dshash_table *hash_table)
     ensure_valid_bucket_pointers(hash_table);
 
     /* Free all the entries. */
-    size = ((size_t) 1) << hash_table->size_log2;
+    size = NUM_BUCKETS(hash_table->size_log2);
     for (i = 0; i < size; ++i)
     {
         dsa_pointer item_pointer = hash_table->buckets[i];
@@ -549,9 +560,14 @@ dshash_delete_entry(dshash_table *hash_table, void *entry)
                                 LW_EXCLUSIVE));
 
     delete_item(hash_table, item);
-    hash_table->find_locked = false;
-    hash_table->find_exclusively_locked = false;
-    LWLockRelease(PARTITION_LOCK(hash_table, partition));
+
+    /* We need to keep partition lock while sequential scan */
+    if (!hash_table->seqscan_running)
+    {
+        hash_table->find_locked = false;
+        hash_table->find_exclusively_locked = false;
+        LWLockRelease(PARTITION_LOCK(hash_table, partition));
+    }
 }
 
 /*
@@ -568,6 +584,8 @@ dshash_release_lock(dshash_table *hash_table, void *entry)
     Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition_index),
                                 hash_table->find_exclusively_locked
                                 ? LW_EXCLUSIVE : LW_SHARED));
+    /* lock is under control of sequential scan */
+    Assert(!hash_table->seqscan_running);
 
     hash_table->find_locked = false;
     hash_table->find_exclusively_locked = false;
@@ -592,6 +610,168 @@ dshash_memhash(const void *v, size_t size, void *arg)
     return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan trhough dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should be called if and only if the scan is abandoned
+ * before completion; if dshash_seq_next returns NULL then it has already done
+ * the end-of-scan cleanup.
+ *
+ * On returning element, it is locked as is the case with dshash_find.
+ * However, the caller must not release the lock. The lock is released as
+ * necessary in continued scan.
+ *
+ * As opposed to the equivalent for dynanash, the caller is not supposed to
+ * delete the returned element before continuing the scan.
+ *
+ * If consistent is set for dshash_seq_init, the whole hash table is
+ * non-exclusively locked. Otherwise a part of the hash table is locked in the
+ * same mode (partition lock).
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+                bool consistent, bool exclusive)
+{
+    /* allowed at most one scan at once */
+    Assert(!hash_table->seqscan_running);
+
+    status->hash_table = hash_table;
+    status->curbucket = 0;
+    status->nbuckets = 0;
+    status->curitem = NULL;
+    status->pnextitem = InvalidDsaPointer;
+    status->curpartition = -1;
+    status->consistent = consistent;
+    status->exclusive = exclusive;
+    hash_table->seqscan_running = true;
+
+    /*
+     * Protect all partitions from modification if the caller wants a
+     * consistent result.
+     */
+    if (consistent)
+    {
+        int i;
+
+        for (i = 0; i < DSHASH_NUM_PARTITIONS; ++i)
+        {
+            Assert(!LWLockHeldByMe(PARTITION_LOCK(hash_table, i)));
+
+            LWLockAcquire(PARTITION_LOCK(hash_table, i),
+                          exclusive ? LW_EXCLUSIVE : LW_SHARED);
+        }
+        ensure_valid_bucket_pointers(hash_table);
+    }
+}
+
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+    dsa_pointer next_item_pointer;
+
+    Assert(status->hash_table->seqscan_running);
+    if (status->curitem == NULL)
+    {
+        int partition;
+
+        Assert (status->curbucket == 0);
+        Assert(!status->hash_table->find_locked);
+
+        /* first shot. grab the first item. */
+        if (!status->consistent)
+        {
+            partition =
+                PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+                                           status->hash_table->size_log2);
+            LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+                          status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+            status->curpartition = partition;
+
+            /* resize doesn't happen from now until seq scan ends */
+            status->nbuckets =
+                NUM_BUCKETS(status->hash_table->control->size_log2);
+            ensure_valid_bucket_pointers(status->hash_table);
+        }
+
+        next_item_pointer = status->hash_table->buckets[status->curbucket];
+    }
+    else
+        next_item_pointer = status->pnextitem;
+
+    /* Move to the next bucket if we finished the current bucket */
+    while (!DsaPointerIsValid(next_item_pointer))
+    {
+        if (++status->curbucket >= status->nbuckets)
+        {
+            /* all buckets have been scanned. finsih. */
+            dshash_seq_term(status);
+            return NULL;
+        }
+
+        /* Also move parititon lock if needed */
+        if (!status->consistent)
+        {
+            int next_partition =
+                PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+                                           status->hash_table->size_log2);
+
+            /* Move lock along with partition for the bucket */
+            if (status->curpartition != next_partition)
+            {
+                /*
+                 * Take lock on the next partition then release the current,
+                 * not in the reverse order. This is required to avoid
+                 * resizing from happening during a sequential scan. Locks are
+                 * taken in partition order so no dead lock happen with other
+                 * seq scans or resizing.
+                 */
+                LWLockAcquire(PARTITION_LOCK(status->hash_table,
+                                             next_partition),
+                              status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+                LWLockRelease(PARTITION_LOCK(status->hash_table,
+                                             status->curpartition));
+                status->curpartition = next_partition;
+            }
+        }
+
+        next_item_pointer = status->hash_table->buckets[status->curbucket];
+    }
+
+    status->curitem =
+        dsa_get_address(status->hash_table->area, next_item_pointer);
+    status->hash_table->find_locked = true;
+    status->hash_table->find_exclusively_locked = status->exclusive;
+
+    /*
+     * This item can be deleted by the caller. Store the next item for the
+     * next iteration for the occasion.
+     */
+    status->pnextitem = status->curitem->next;
+
+    return ENTRY_FROM_ITEM(status->curitem);
+}
+
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+    Assert(status->hash_table->seqscan_running);
+    status->hash_table->find_locked = false;
+    status->hash_table->find_exclusively_locked = false;
+    status->hash_table->seqscan_running = false;
+
+    if (status->consistent)
+    {
+        int i;
+
+        for (i = 0; i < DSHASH_NUM_PARTITIONS; ++i)
+            LWLockRelease(PARTITION_LOCK(status->hash_table, i));
+    }
+    else if (status->curpartition >= 0)
+        LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index e5dfd57f0a..b80f3af995 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,23 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state of dshash. The detail is exposed since the storage
+ * size should be known to users but it should be considered as an opaque
+ * type by callers.
+ */
+typedef struct dshash_seq_status
+{
+    dshash_table       *hash_table;
+    int                    curbucket;
+    int                    nbuckets;
+    dshash_table_item  *curitem;
+    dsa_pointer            pnextitem;
+    int                    curpartition;
+    bool                consistent;
+    bool                exclusive;
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
               const dshash_parameters *params,
@@ -70,7 +87,6 @@ extern dshash_table *dshash_attach(dsa_area *area,
 extern void dshash_detach(dshash_table *hash_table);
 extern dshash_table_handle dshash_get_hash_table_handle(dshash_table *hash_table);
 extern void dshash_destroy(dshash_table *hash_table);
-
 /* Finding, creating, deleting entries. */
 extern void *dshash_find(dshash_table *hash_table,
             const void *key, bool exclusive);
@@ -80,6 +96,11 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+                            bool consistent, bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int    dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
-- 
2.16.3

From cbd96a824d077b8ea5b77dc8a8c3fc1f4d4e74a9 Mon Sep 17 00:00:00 2001
From: Kyotaro Horiguchi <horiguchi.kyotaro@lab.ntt.co.jp>
Date: Thu, 27 Sep 2018 11:15:19 +0900
Subject: [PATCH 2/6] Add conditional lock feature to dshash

Dshash currently waits for lock unconditionally. This commit adds new
interfaces for dshash_find and dshash_find_or_insert. The new
interfaces have an extra parameter "nowait" taht commands not to wait
for lock.
---
 src/backend/lib/dshash.c | 69 +++++++++++++++++++++++++++++++++++++++++++-----
 src/include/lib/dshash.h |  4 +++
 2 files changed, 66 insertions(+), 7 deletions(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index 1e8c22f94f..303210e326 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -394,19 +394,48 @@ dshash_get_hash_table_handle(dshash_table *hash_table)
  */
 void *
 dshash_find(dshash_table *hash_table, const void *key, bool exclusive)
+{
+    return dshash_find_extended(hash_table, key, exclusive, false, NULL);
+}
+
+/*
+ * Addition to dshash_find, returns immediately when nowait is true and lock
+ * was not acquired. Lock status is set to *lock_failed if any.
+ */
+void *
+dshash_find_extended(dshash_table *hash_table, const void *key,
+                     bool exclusive, bool nowait, bool *lock_acquired)
 {
     dshash_hash hash;
     size_t        partition;
     dshash_table_item *item;
 
+    /* allowing !nowait returning the result is just not sensible */
+    Assert(nowait || !lock_acquired);
+
     hash = hash_key(hash_table, key);
     partition = PARTITION_FOR_HASH(hash);
 
     Assert(hash_table->control->magic == DSHASH_MAGIC);
     Assert(!hash_table->find_locked);
 
-    LWLockAcquire(PARTITION_LOCK(hash_table, partition),
-                  exclusive ? LW_EXCLUSIVE : LW_SHARED);
+    if (nowait)
+    {
+        if (!LWLockConditionalAcquire(PARTITION_LOCK(hash_table, partition),
+                                      exclusive ? LW_EXCLUSIVE : LW_SHARED))
+        {
+            if (lock_acquired)
+                *lock_acquired = false;
+            return NULL;
+        }
+    }
+    else
+        LWLockAcquire(PARTITION_LOCK(hash_table, partition),
+                      exclusive ? LW_EXCLUSIVE : LW_SHARED);
+
+    if (lock_acquired)
+        *lock_acquired = true;
+
     ensure_valid_bucket_pointers(hash_table);
 
     /* Search the active bucket. */
@@ -441,6 +470,22 @@ void *
 dshash_find_or_insert(dshash_table *hash_table,
                       const void *key,
                       bool *found)
+{
+    return dshash_find_or_insert_extended(hash_table, key, found, false);
+}
+
+/*
+ * Addition to dshash_find_or_insert, returns NULL if nowait is true and lock
+ * was not acquired.
+ *
+ * Notes above dshash_find_extended() regarding locking and error handling
+ * equally apply here.
+ */
+void *
+dshash_find_or_insert_extended(dshash_table *hash_table,
+                               const void *key,
+                               bool *found,
+                               bool nowait)
 {
     dshash_hash hash;
     size_t        partition_index;
@@ -455,8 +500,16 @@ dshash_find_or_insert(dshash_table *hash_table,
     Assert(!hash_table->find_locked);
 
 restart:
-    LWLockAcquire(PARTITION_LOCK(hash_table, partition_index),
-                  LW_EXCLUSIVE);
+    if (nowait)
+    {
+        if (!LWLockConditionalAcquire(
+                PARTITION_LOCK(hash_table, partition_index),
+                LW_EXCLUSIVE))
+            return NULL;
+    }
+    else
+        LWLockAcquire(PARTITION_LOCK(hash_table, partition_index),
+                      LW_EXCLUSIVE);
     ensure_valid_bucket_pointers(hash_table);
 
     /* Search the active bucket. */
@@ -626,9 +679,11 @@ dshash_memhash(const void *v, size_t size, void *arg)
  * As opposed to the equivalent for dynanash, the caller is not supposed to
  * delete the returned element before continuing the scan.
  *
- * If consistent is set for dshash_seq_init, the whole hash table is
- * non-exclusively locked. Otherwise a part of the hash table is locked in the
- * same mode (partition lock).
+ * If consistent is set for dshash_seq_init, the all hash table
+ * partitions are locked in the requested mode (as determined by the
+ * exclusive flag), and the locks are held until the end of the scan.
+ * Otherwise the partition locks are acquired and released as needed
+ * during the scan (up to two partitions may be locked at the same time).
  */
 void
 dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index b80f3af995..21587c07ce 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -90,8 +90,12 @@ extern void dshash_destroy(dshash_table *hash_table);
 /* Finding, creating, deleting entries. */
 extern void *dshash_find(dshash_table *hash_table,
             const void *key, bool exclusive);
+extern void *dshash_find_extended(dshash_table *hash_table, const void *key,
+            bool exclusive, bool nowait, bool *lock_acquired);
 extern void *dshash_find_or_insert(dshash_table *hash_table,
                       const void *key, bool *found);
+extern void *dshash_find_or_insert_extended(dshash_table *hash_table,
+            const void *key, bool *found, bool nowait);
 extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
-- 
2.16.3

From df17a84d5e79f844f1ceafc1ad6c673779800844 Mon Sep 17 00:00:00 2001
From: Kyotaro Horiguchi <horiguchi.kyotaro@lab.ntt.co.jp>
Date: Wed, 7 Nov 2018 16:53:49 +0900
Subject: [PATCH 3/6] Make archiver process an auxiliary process

This is a preliminary patch for shared-memory based stats collector.
Archiver process must be a auxiliary process since it uses shared
memory after stats data wes moved onto shared-memory. Make the process
an auxiliary process in order to make it work.
---
 src/backend/bootstrap/bootstrap.c   |  8 +++
 src/backend/postmaster/pgarch.c     | 98 +++++++++----------------------------
 src/backend/postmaster/pgstat.c     |  6 +++
 src/backend/postmaster/postmaster.c | 35 +++++++++----
 src/include/miscadmin.h             |  2 +
 src/include/pgstat.h                |  1 +
 src/include/postmaster/pgarch.h     |  4 +-
 7 files changed, 67 insertions(+), 87 deletions(-)

diff --git a/src/backend/bootstrap/bootstrap.c b/src/backend/bootstrap/bootstrap.c
index 4d7ed8ad1a..b0878a3dd9 100644
--- a/src/backend/bootstrap/bootstrap.c
+++ b/src/backend/bootstrap/bootstrap.c
@@ -328,6 +328,9 @@ AuxiliaryProcessMain(int argc, char *argv[])
             case BgWriterProcess:
                 statmsg = pgstat_get_backend_desc(B_BG_WRITER);
                 break;
+            case ArchiverProcess:
+                statmsg = pgstat_get_backend_desc(B_ARCHIVER);
+                break;
             case CheckpointerProcess:
                 statmsg = pgstat_get_backend_desc(B_CHECKPOINTER);
                 break;
@@ -455,6 +458,11 @@ AuxiliaryProcessMain(int argc, char *argv[])
             BackgroundWriterMain();
             proc_exit(1);        /* should never return */
 
+        case ArchiverProcess:
+            /* don't set signals, archiver has its own agenda */
+            PgArchiverMain();
+            proc_exit(1);        /* should never return */
+
         case CheckpointerProcess:
             /* don't set signals, checkpointer has its own agenda */
             CheckpointerMain();
diff --git a/src/backend/postmaster/pgarch.c b/src/backend/postmaster/pgarch.c
index f84f882c4c..4342ebdab4 100644
--- a/src/backend/postmaster/pgarch.c
+++ b/src/backend/postmaster/pgarch.c
@@ -77,7 +77,6 @@
  * Local data
  * ----------
  */
-static time_t last_pgarch_start_time;
 static time_t last_sigterm_time = 0;
 
 /*
@@ -96,7 +95,6 @@ static volatile sig_atomic_t ready_to_stop = false;
 static pid_t pgarch_forkexec(void);
 #endif
 
-NON_EXEC_STATIC void PgArchiverMain(int argc, char *argv[]) pg_attribute_noreturn();
 static void pgarch_exit(SIGNAL_ARGS);
 static void ArchSigHupHandler(SIGNAL_ARGS);
 static void ArchSigTermHandler(SIGNAL_ARGS);
@@ -114,75 +112,6 @@ static void pgarch_archiveDone(char *xlog);
  * ------------------------------------------------------------
  */
 
-/*
- * pgarch_start
- *
- *    Called from postmaster at startup or after an existing archiver
- *    died.  Attempt to fire up a fresh archiver process.
- *
- *    Returns PID of child process, or 0 if fail.
- *
- *    Note: if fail, we will be called again from the postmaster main loop.
- */
-int
-pgarch_start(void)
-{
-    time_t        curtime;
-    pid_t        pgArchPid;
-
-    /*
-     * Do nothing if no archiver needed
-     */
-    if (!XLogArchivingActive())
-        return 0;
-
-    /*
-     * Do nothing if too soon since last archiver start.  This is a safety
-     * valve to protect against continuous respawn attempts if the archiver is
-     * dying immediately at launch. Note that since we will be re-called from
-     * the postmaster main loop, we will get another chance later.
-     */
-    curtime = time(NULL);
-    if ((unsigned int) (curtime - last_pgarch_start_time) <
-        (unsigned int) PGARCH_RESTART_INTERVAL)
-        return 0;
-    last_pgarch_start_time = curtime;
-
-#ifdef EXEC_BACKEND
-    switch ((pgArchPid = pgarch_forkexec()))
-#else
-    switch ((pgArchPid = fork_process()))
-#endif
-    {
-        case -1:
-            ereport(LOG,
-                    (errmsg("could not fork archiver: %m")));
-            return 0;
-
-#ifndef EXEC_BACKEND
-        case 0:
-            /* in postmaster child ... */
-            InitPostmasterChild();
-
-            /* Close the postmaster's sockets */
-            ClosePostmasterPorts(false);
-
-            /* Drop our connection to postmaster's shared memory, as well */
-            dsm_detach_all();
-            PGSharedMemoryDetach();
-
-            PgArchiverMain(0, NULL);
-            break;
-#endif
-
-        default:
-            return (int) pgArchPid;
-    }
-
-    /* shouldn't get here */
-    return 0;
-}
-
 /* ------------------------------------------------------------
  * Local functions called by archiver follow
  * ------------------------------------------------------------
@@ -222,8 +151,8 @@ pgarch_forkexec(void)
  *    The argc/argv parameters are valid only in EXEC_BACKEND case.  However,
  *    since we don't use 'em, it hardly matters...
  */
-NON_EXEC_STATIC void
-PgArchiverMain(int argc, char *argv[])
+void
+PgArchiverMain(void)
 {
     /*
      * Ignore all signals usually bound to some action in the postmaster,
@@ -255,8 +184,27 @@ PgArchiverMain(int argc, char *argv[])
 static void
 pgarch_exit(SIGNAL_ARGS)
 {
-    /* SIGQUIT means curl up and die ... */
-    exit(1);
+    PG_SETMASK(&BlockSig);
+
+    /*
+     * We DO NOT want to run proc_exit() callbacks -- we're here because
+     * shared memory may be corrupted, so we don't want to try to clean up our
+     * transaction.  Just nail the windows shut and get out of town.  Now that
+     * there's an atexit callback to prevent third-party code from breaking
+     * things by calling exit() directly, we have to reset the callbacks
+     * explicitly to make this work as intended.
+     */
+    on_exit_reset();
+
+    /*
+     * Note we do exit(2) not exit(0).  This is to force the postmaster into a
+     * system reset cycle if some idiot DBA sends a manual SIGQUIT to a random
+     * backend.  This is necessary precisely because we don't clean up our
+     * shared memory state.  (The "dead man switch" mechanism in pmsignal.c
+     * should ensure the postmaster sees this as a crash, too, but no harm in
+     * being doubly sure.)
+     */
+    exit(2);
 }
 
 /* SIGHUP signal handler for archiver process */
diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index 81c6499251..8d3c45dd4e 100644
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -2856,6 +2856,9 @@ pgstat_bestart(void)
             case BgWriterProcess:
                 beentry->st_backendType = B_BG_WRITER;
                 break;
+            case ArchiverProcess:
+                beentry->st_backendType = B_ARCHIVER;
+                break;
             case CheckpointerProcess:
                 beentry->st_backendType = B_CHECKPOINTER;
                 break;
@@ -4105,6 +4108,9 @@ pgstat_get_backend_desc(BackendType backendType)
 
     switch (backendType)
     {
+        case B_ARCHIVER:
+            backendDesc = "archiver";
+            break;
         case B_AUTOVAC_LAUNCHER:
             backendDesc = "autovacuum launcher";
             break;
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index ccea231e98..820f356038 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -146,7 +146,8 @@
 #define BACKEND_TYPE_AUTOVAC    0x0002    /* autovacuum worker process */
 #define BACKEND_TYPE_WALSND        0x0004    /* walsender process */
 #define BACKEND_TYPE_BGWORKER    0x0008    /* bgworker process */
-#define BACKEND_TYPE_ALL        0x000F    /* OR of all the above */
+#define BACKEND_TYPE_ARCHIVER    0x0010    /* archiver process */
+#define BACKEND_TYPE_ALL        0x001F    /* OR of all the above */
 
 #define BACKEND_TYPE_WORKER        (BACKEND_TYPE_AUTOVAC | BACKEND_TYPE_BGWORKER)
 
@@ -538,6 +539,7 @@ static void ShmemBackendArrayRemove(Backend *bn);
 #endif                            /* EXEC_BACKEND */
 
 #define StartupDataBase()        StartChildProcess(StartupProcess)
+#define StartArchiver()            StartChildProcess(ArchiverProcess)
 #define StartBackgroundWriter() StartChildProcess(BgWriterProcess)
 #define StartCheckpointer()        StartChildProcess(CheckpointerProcess)
 #define StartWalWriter()        StartChildProcess(WalWriterProcess)
@@ -1761,7 +1763,7 @@ ServerLoop(void)
 
         /* If we have lost the archiver, try to start a new one. */
         if (PgArchPID == 0 && PgArchStartupAllowed())
-            PgArchPID = pgarch_start();
+            PgArchPID = StartArchiver();
 
         /* If we need to signal the autovacuum launcher, do so now */
         if (avlauncher_needs_signal)
@@ -2924,7 +2926,7 @@ reaper(SIGNAL_ARGS)
             if (!IsBinaryUpgrade && AutoVacuumingActive() && AutoVacPID == 0)
                 AutoVacPID = StartAutoVacLauncher();
             if (PgArchStartupAllowed() && PgArchPID == 0)
-                PgArchPID = pgarch_start();
+                PgArchPID = StartArchiver();
             if (PgStatPID == 0)
                 PgStatPID = pgstat_start();
 
@@ -3069,10 +3071,8 @@ reaper(SIGNAL_ARGS)
         {
             PgArchPID = 0;
             if (!EXIT_STATUS_0(exitstatus))
-                LogChildExit(LOG, _("archiver process"),
-                             pid, exitstatus);
-            if (PgArchStartupAllowed())
-                PgArchPID = pgarch_start();
+                HandleChildCrash(pid, exitstatus,
+                                 _("archiver process"));
             continue;
         }
 
@@ -3318,7 +3318,7 @@ CleanupBackend(int pid,
 
 /*
  * HandleChildCrash -- cleanup after failed backend, bgwriter, checkpointer,
- * walwriter, autovacuum, or background worker.
+ * walwriter, autovacuum, archiver or background worker.
  *
  * The objectives here are to clean up our local state about the child
  * process, and to signal all other remaining children to quickdie.
@@ -3523,6 +3523,18 @@ HandleChildCrash(int pid, int exitstatus, const char *procname)
         signal_child(AutoVacPID, (SendStop ? SIGSTOP : SIGQUIT));
     }
 
+    /* Take care of the archiver too */
+    if (pid == PgArchPID)
+        PgArchPID = 0;
+    else if (PgArchPID != 0 && take_action)
+    {
+        ereport(DEBUG2,
+                (errmsg_internal("sending %s to process %d",
+                                 (SendStop ? "SIGSTOP" : "SIGQUIT"),
+                                 (int) PgArchPID)));
+        signal_child(PgArchPID, (SendStop ? SIGSTOP : SIGQUIT));
+    }
+
     /*
      * Force a power-cycle of the pgarch process too.  (This isn't absolutely
      * necessary, but it seems like a good idea for robustness, and it
@@ -3799,6 +3811,7 @@ PostmasterStateMachine(void)
             Assert(CheckpointerPID == 0);
             Assert(WalWriterPID == 0);
             Assert(AutoVacPID == 0);
+            Assert(PgArchPID == 0);
             /* syslogger is not considered here */
             pmState = PM_NO_CHILDREN;
         }
@@ -5068,7 +5081,7 @@ sigusr1_handler(SIGNAL_ARGS)
          */
         Assert(PgArchPID == 0);
         if (XLogArchivingAlways())
-            PgArchPID = pgarch_start();
+            PgArchPID = StartArchiver();
 
         /*
          * If we aren't planning to enter hot standby mode later, treat
@@ -5342,6 +5355,10 @@ StartChildProcess(AuxProcType type)
                 ereport(LOG,
                         (errmsg("could not fork startup process: %m")));
                 break;
+            case ArchiverProcess:
+                ereport(LOG,
+                        (errmsg("could not fork archiver process: %m")));
+                break;
             case BgWriterProcess:
                 ereport(LOG,
                         (errmsg("could not fork background writer process: %m")));
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index c9e35003a5..63a7653457 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -399,6 +399,7 @@ typedef enum
     BootstrapProcess,
     StartupProcess,
     BgWriterProcess,
+    ArchiverProcess,
     CheckpointerProcess,
     WalWriterProcess,
     WalReceiverProcess,
@@ -411,6 +412,7 @@ extern AuxProcType MyAuxProcType;
 #define AmBootstrapProcess()        (MyAuxProcType == BootstrapProcess)
 #define AmStartupProcess()            (MyAuxProcType == StartupProcess)
 #define AmBackgroundWriterProcess() (MyAuxProcType == BgWriterProcess)
+#define AmArchiverProcess()            (MyAuxProcType == ArchiverProcess)
 #define AmCheckpointerProcess()        (MyAuxProcType == CheckpointerProcess)
 #define AmWalWriterProcess()        (MyAuxProcType == WalWriterProcess)
 #define AmWalReceiverProcess()        (MyAuxProcType == WalReceiverProcess)
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index 88a75fb798..3324be8a81 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -701,6 +701,7 @@ typedef struct PgStat_GlobalStats
  */
 typedef enum BackendType
 {
+    B_ARCHIVER,
     B_AUTOVAC_LAUNCHER,
     B_AUTOVAC_WORKER,
     B_BACKEND,
diff --git a/src/include/postmaster/pgarch.h b/src/include/postmaster/pgarch.h
index 2474eac26a..88f16863d4 100644
--- a/src/include/postmaster/pgarch.h
+++ b/src/include/postmaster/pgarch.h
@@ -32,8 +32,6 @@
  */
 extern int    pgarch_start(void);
 
-#ifdef EXEC_BACKEND
-extern void PgArchiverMain(int argc, char *argv[]) pg_attribute_noreturn();
-#endif
+extern void PgArchiverMain(void) pg_attribute_noreturn();
 
 #endif                            /* _PGARCH_H */
-- 
2.16.3

From a0c8ff34a3e247d13869ce4507fe44b34fa47507 Mon Sep 17 00:00:00 2001
From: Kyotaro Horiguchi <horiguchi.kyotaro@lab.ntt.co.jp>
Date: Thu, 21 Feb 2019 12:42:07 +0900
Subject: [PATCH 4/6] Allow dsm to use on postmaster.

DSM is inhibited to be used on postmaster. Shared memory baesd stats
collector needs it to work on postmaster and no problem found to do
that. Just allow it.
---
 src/backend/storage/ipc/dsm.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/src/backend/storage/ipc/dsm.c b/src/backend/storage/ipc/dsm.c
index 23ccc59f13..d30a876bb0 100644
--- a/src/backend/storage/ipc/dsm.c
+++ b/src/backend/storage/ipc/dsm.c
@@ -440,8 +440,7 @@ dsm_create(Size size, int flags)
     uint32        i;
     uint32        nitems;
 
-    /* Unsafe in postmaster (and pointless in a stand-alone backend). */
-    Assert(IsUnderPostmaster);
+    Assert(dsm_control != NULL);
 
     if (!dsm_init_done)
         dsm_backend_startup();
@@ -537,8 +536,7 @@ dsm_attach(dsm_handle h)
     uint32        i;
     uint32        nitems;
 
-    /* Unsafe in postmaster (and pointless in a stand-alone backend). */
-    Assert(IsUnderPostmaster);
+    Assert(dsm_control != NULL);
 
     if (!dsm_init_done)
         dsm_backend_startup();
-- 
2.16.3

From 5259e756167e8cd355d8c53826f64178fc8d14b8 Mon Sep 17 00:00:00 2001
From: Kyotaro Horiguchi <horiguchi.kyotaro@lab.ntt.co.jp>
Date: Thu, 21 Feb 2019 12:44:56 +0900
Subject: [PATCH 5/6] Shared-memory based stats collector

Previously activity statistics is shared via files on disk. Every
backend sends the numbers to the stats collector process via a socket.
It makes snapshots as a set of files on disk with a certain interval
then every backend reads them as necessary. It worked fine for
comparatively small set of statistics but the set is under the
pressure to growing up and the file size has reached the order of
megabytes. To deal with larger statistics set, this patch let backends
directly share the statistics via shared memory.
---
 doc/src/sgml/monitoring.sgml                 |    6 +-
 src/backend/postmaster/autovacuum.c          |    6 +-
 src/backend/postmaster/pgstat.c              | 5435 +++++++++++---------------
 src/backend/postmaster/postmaster.c          |   85 +-
 src/backend/storage/ipc/ipci.c               |    6 +
 src/backend/storage/lmgr/lwlock.c            |    1 +
 src/backend/tcop/postgres.c                  |   27 +-
 src/backend/utils/init/globals.c             |    1 +
 src/backend/utils/init/postinit.c            |   11 +
 src/bin/pg_basebackup/t/010_pg_basebackup.pl |    2 +-
 src/include/miscadmin.h                      |    1 +
 src/include/pgstat.h                         |  469 +--
 src/include/storage/lwlock.h                 |    1 +
 src/include/utils/timeout.h                  |    1 +
 14 files changed, 2478 insertions(+), 3574 deletions(-)

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 5c1408bdf5..83a0be1965 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -53,7 +53,6 @@ postgres  15554  0.0  0.0  57536  1184 ?        Ss   18:02   0:00 postgres: back
 postgres  15555  0.0  0.0  57536   916 ?        Ss   18:02   0:00 postgres: checkpointer
 postgres  15556  0.0  0.0  57536   916 ?        Ss   18:02   0:00 postgres: walwriter
 postgres  15557  0.0  0.0  58504  2244 ?        Ss   18:02   0:00 postgres: autovacuum launcher
-postgres  15558  0.0  0.0  17512  1068 ?        Ss   18:02   0:00 postgres: stats collector
 postgres  15582  0.0  0.0  58772  3080 ?        Ss   18:04   0:00 postgres: joe runbug 127.0.0.1 idle
 postgres  15606  0.0  0.0  58772  3052 ?        Ss   18:07   0:00 postgres: tgl regression [local] SELECT waiting
 postgres  15610  0.0  0.0  58772  3056 ?        Ss   18:07   0:00 postgres: tgl regression [local] idle in
transaction
@@ -65,9 +64,8 @@ postgres  15610  0.0  0.0  58772  3056 ?        Ss   18:07   0:00 postgres: tgl
    master server process.  The command arguments
    shown for it are the same ones used when it was launched.  The next five
    processes are background worker processes automatically launched by the
-   master process.  (The <quote>stats collector</quote> process will not be present
-   if you have set the system not to start the statistics collector; likewise
-   the <quote>autovacuum launcher</quote> process can be disabled.)
+   master process.  (The <quote>autovacuum launcher</quote> process will not
+   be present if you have set the system not to start it.)
    Each of the remaining
    processes is a server process handling one client connection.  Each such
    process sets its command line display in the form
diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index d1177b3855..1b7429217a 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -2749,12 +2749,10 @@ get_pgstat_tabentry_relid(Oid relid, bool isshared, PgStat_StatDBEntry *shared,
     if (isshared)
     {
         if (PointerIsValid(shared))
-            tabentry = hash_search(shared->tables, &relid,
-                                   HASH_FIND, NULL);
+            tabentry = pgstat_fetch_stat_tabentry_extended(shared, relid);
     }
     else if (PointerIsValid(dbentry))
-        tabentry = hash_search(dbentry->tables, &relid,
-                               HASH_FIND, NULL);
+        tabentry = pgstat_fetch_stat_tabentry_extended(dbentry, relid);
 
     return tabentry;
 }
diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index 8d3c45dd4e..ba4c274f9a 100644
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -1,15 +1,19 @@
 /* ----------
  * pgstat.c
  *
- *    All the statistics collector stuff hacked up in one big, ugly file.
+ *    Statistics collector facility.
  *
- *    TODO:    - Separate collector, postmaster and backend stuff
- *              into different files.
- *
- *            - Add some automatic call for pgstat vacuuming.
- *
- *            - Add a pgstat config column to pg_database, so this
- *              entire thing can be enabled/disabled on a per db basis.
+ *  Collects per-table and per-function usage statistics of backends and shares
+ *  them among all backends via shared memory. Every backend records
+ *  individual activity in local memory using pg_count_*() and friends
+ *  interfaces during a transaction. Then pgstat_report_stat() is called at
+ *  the end of a transaction to flush out the local numbers to shared
+ *  memory. To avoid congestion on the shared memory, we do that not often
+ *  than PGSTAT_STAT_MIN_INTERVAL(500ms). Still it is possible that a backend
+ *  cannot flush all or a part of local numbers immediately, such numbers are
+ *  postponed to the next chances with the interval of
+ *  PGSTAT_STAT_RETRY_INTERVAL(100ms), but they are not kept longer than
+ *  PGSTAT_STAT_MAX_INTERVAL(1000ms).
  *
  *    Copyright (c) 2001-2019, PostgreSQL Global Development Group
  *
@@ -19,88 +23,47 @@
 #include "postgres.h"
 
 #include <unistd.h>
-#include <fcntl.h>
-#include <sys/param.h>
-#include <sys/time.h>
-#include <sys/socket.h>
-#include <netdb.h>
-#include <netinet/in.h>
-#include <arpa/inet.h>
-#include <signal.h>
-#include <time.h>
-#ifdef HAVE_SYS_SELECT_H
-#include <sys/select.h>
-#endif
 
 #include "pgstat.h"
 
 #include "access/heapam.h"
 #include "access/htup_details.h"
-#include "access/transam.h"
 #include "access/twophase_rmgr.h"
 #include "access/xact.h"
 #include "catalog/pg_database.h"
 #include "catalog/pg_proc.h"
-#include "common/ip.h"
 #include "libpq/libpq.h"
-#include "libpq/pqsignal.h"
-#include "mb/pg_wchar.h"
 #include "miscadmin.h"
-#include "pg_trace.h"
 #include "postmaster/autovacuum.h"
-#include "postmaster/fork_process.h"
-#include "postmaster/postmaster.h"
 #include "replication/walsender.h"
-#include "storage/backendid.h"
-#include "storage/dsm.h"
-#include "storage/fd.h"
 #include "storage/ipc.h"
-#include "storage/latch.h"
 #include "storage/lmgr.h"
-#include "storage/pg_shmem.h"
+#include "storage/proc.h"
 #include "storage/procsignal.h"
 #include "storage/sinvaladt.h"
 #include "utils/ascii.h"
 #include "utils/guc.h"
 #include "utils/memutils.h"
-#include "utils/ps_status.h"
-#include "utils/rel.h"
+#include "utils/probes.h"
 #include "utils/snapmgr.h"
-#include "utils/timestamp.h"
-
 
 /* ----------
  * Timer definitions.
  * ----------
  */
-#define PGSTAT_STAT_INTERVAL    500 /* Minimum time between stats file
-                                     * updates; in milliseconds. */
+#define PGSTAT_STAT_MIN_INTERVAL    500 /* Minimum time between stats data
+                                         * updates; in milliseconds. */
 
-#define PGSTAT_RETRY_DELAY        10    /* How long to wait between checks for a
-                                     * new file; in milliseconds. */
-
-#define PGSTAT_MAX_WAIT_TIME    10000    /* Maximum time to wait for a stats
-                                         * file update; in milliseconds. */
-
-#define PGSTAT_INQ_INTERVAL        640 /* How often to ping the collector for a
-                                     * new file; in milliseconds. */
-
-#define PGSTAT_RESTART_INTERVAL 60    /* How often to attempt to restart a
-                                     * failed statistics collector; in
-                                     * seconds. */
-
-#define PGSTAT_POLL_LOOP_COUNT    (PGSTAT_MAX_WAIT_TIME / PGSTAT_RETRY_DELAY)
-#define PGSTAT_INQ_LOOP_COUNT    (PGSTAT_INQ_INTERVAL / PGSTAT_RETRY_DELAY)
-
-/* Minimum receive buffer size for the collector's socket. */
-#define PGSTAT_MIN_RCVBUF        (100 * 1024)
+#define PGSTAT_STAT_RETRY_INTERVAL    100 /* Retry interval between after
+                                         * elapsed PGSTAT_MIN_INTERVAL*/
 
+#define PGSTAT_STAT_MAX_INTERVAL   1000 /* Maximum time between stats data
+                                         * updates; in milliseconds. */
 
 /* ----------
  * The initial size hints for the hash tables used in the collector.
  * ----------
  */
-#define PGSTAT_DB_HASH_SIZE        16
 #define PGSTAT_TAB_HASH_SIZE    512
 #define PGSTAT_FUNCTION_HASH_SIZE    512
 
@@ -116,6 +79,19 @@
  */
 #define NumBackendStatSlots (MaxBackends + NUM_AUXPROCTYPES)
 
+/*
+ * Operation mode of pgstat_get_db_entry.
+ */
+#define    PGSTAT_FETCH_SHARED        0
+#define    PGSTAT_FETCH_EXCLUSIVE    1
+#define    PGSTAT_FETCH_NOWAIT        2
+
+typedef enum PgStat_TableLookupState
+{
+    PGSTAT_ENTRY_NOT_FOUND,
+    PGSTAT_ENTRY_FOUND,
+    PGSTAT_ENTRY_LOCK_FAILED
+} PgStat_TableLookupState;
 
 /* ----------
  * GUC parameters
@@ -131,9 +107,23 @@ int            pgstat_track_activity_query_size = 1024;
  * ----------
  */
 char       *pgstat_stat_directory = NULL;
+
+/* No longer used, but will be removed with GUC */
 char       *pgstat_stat_filename = NULL;
 char       *pgstat_stat_tmpname = NULL;
 
+LWLock        StatsMainLock;
+#define        StatsLock (&StatsMainLock)
+
+/* Shared stats bootstrap information */
+typedef struct StatsShmemStruct {
+    dsa_handle stats_dsa_handle;
+    dshash_table_handle db_hash_handle;
+    dsa_pointer    global_stats;
+    dsa_pointer    archiver_stats;
+    TimestampTz last_update;
+} StatsShmemStruct;
+
 /*
  * BgWriter global statistics counters (unused in other processes).
  * Stored directly in a stats message structure so it can be sent
@@ -145,17 +135,38 @@ PgStat_MsgBgWriter BgWriterStats;
  * Local data
  * ----------
  */
-NON_EXEC_STATIC pgsocket pgStatSock = PGINVALID_SOCKET;
+/* Variables lives for the backend lifetime */
+static StatsShmemStruct * StatsShmem = NULL;
+static dsa_area *area = NULL;
+static dshash_table *pgStatDBHash;
+static MemoryContext pgSharedStatsContext = NULL;
 
-static struct sockaddr_storage pgStatAddr;
-
-static time_t last_pgstat_start_time;
-
-static bool pgStatRunningInCollector = false;
+/* dshash parameter for each type of table */
+static const dshash_parameters dsh_dbparams = {
+    sizeof(Oid),
+    sizeof(PgStat_StatDBEntry),
+    dshash_memcmp,
+    dshash_memhash,
+    LWTRANCHE_STATS
+};
+static const dshash_parameters dsh_tblparams = {
+    sizeof(Oid),
+    sizeof(PgStat_StatTabEntry),
+    dshash_memcmp,
+    dshash_memhash,
+    LWTRANCHE_STATS
+};
+static const dshash_parameters dsh_funcparams = {
+    sizeof(Oid),
+    sizeof(PgStat_StatFuncEntry),
+    dshash_memcmp,
+    dshash_memhash,
+    LWTRANCHE_STATS
+};
 
 /*
  * Structures in which backends store per-table info that's waiting to be
- * sent to the collector.
+ * written to shared memory.
  *
  * NOTE: once allocated, TabStatusArray structures are never moved or deleted
  * for the life of the backend.  Also, we zero out the t_id fields of the
@@ -190,8 +201,8 @@ typedef struct TabStatHashEntry
 static HTAB *pgStatTabHash = NULL;
 
 /*
- * Backends store per-function info that's waiting to be sent to the collector
- * in this hash table (indexed by function OID).
+ * Backends store per-function info that's waiting to be flushed out to shared
+ * memory in this hash table (indexed by function OID).
  */
 static HTAB *pgStatFunctions = NULL;
 
@@ -201,6 +212,46 @@ static HTAB *pgStatFunctions = NULL;
  */
 static bool have_function_stats = false;
 
+/* dbentry has some additional data in snapshot */
+typedef struct PgStat_StatDBEntry_snapshot
+{
+    PgStat_StatDBEntry shared_part;
+
+    HTAB *snapshot_tables;                /* table entry snapshot */
+    HTAB *snapshot_functions;            /* function entry snapshot */
+    dshash_table    *dshash_tables;        /* attached tables dshash */
+    dshash_table    *dshash_functions;    /* attached functions dshash */
+} PgStat_StatDBEntry_snapshot;
+
+/* context struct for snapshot_statentry */
+typedef struct pgstat_snapshot_cxt
+{
+    char           *hash_name;            /* name of the snapshot hash */
+    HTAB          **hash;                /* placeholder for the hash */
+    int                hash_entsize;        /* element size of hash entry */
+    dshash_table  **dshash;                /* placeholder for attached dshash */
+    dshash_table_handle    dsh_handle;        /* dsh handle to attach */
+    const dshash_parameters *dsh_params;/* dshash params */
+} pgstat_snapshot_cxt;
+
+/*
+ *  Backends store various database-wide info that's waiting to be flushed out
+ *  to shared memory in these variables.
+ */
+static int        n_deadlocks = 0;
+static size_t    n_tmpfiles = 0;
+static size_t    n_tmpfilesize = 0;
+
+/*
+ * have_recovery_conflicts represents the existence of any kind if conflict
+ */
+static bool        have_recovery_conflicts = false;
+static int        n_conflict_tablespace = 0;
+static int        n_conflict_lock = 0;
+static int        n_conflict_snapshot = 0;
+static int        n_conflict_bufferpin = 0;
+static int        n_conflict_startup_deadlock = 0;
+
 /*
  * Tuple insertion/deletion counts for an open transaction can't be propagated
  * into PgStat_TableStatus counters until we know if it is going to commit
@@ -236,36 +287,41 @@ typedef struct TwoPhasePgStatRecord
     bool        t_truncated;    /* was the relation truncated? */
 } TwoPhasePgStatRecord;
 
-/*
- * Info about current "snapshot" of stats file
- */
+/* Variables for backend status snapshot. The snapshot includes auxiliary. */
 static MemoryContext pgStatLocalContext = NULL;
-static HTAB *pgStatDBHash = NULL;
-
-/* Status for backends including auxiliary */
 static LocalPgBackendStatus *localBackendStatusTable = NULL;
-
-/* Total number of backends including auxiliary */
 static int    localNumBackends = 0;
 
-/*
- * Cluster wide statistics, kept in the stats collector.
- * Contains statistics that are not collected per database
- * or per table.
- */
-static PgStat_ArchiverStats archiverStats;
-static PgStat_GlobalStats globalStats;
+/* Variables for activity statistics snapshot. */
+static MemoryContext pgStatSnapshotContext = NULL;
+static HTAB *pgStatDBEntrySnapshot;
+static TimestampTz snapshot_expires_at = 0; /* local cache expiration time */
+static bool        first_in_xact = true;      /* is the first time in this xact? */
+
+
+/* Context struct for flushing to shared memory */
+typedef struct pgstat_flush_stat_context
+{
+    int    shgeneration;
+    PgStat_StatDBEntry *shdbentry;
+    dshash_table *shdb_tabhash;
+
+    int    mygeneration;
+    PgStat_StatDBEntry *mydbentry;
+    dshash_table *mydb_tabhash;
+} pgstat_flush_stat_context;
 
 /*
- * List of OIDs of databases we need to write out.  If an entry is InvalidOid,
- * it means to write only the shared-catalog stats ("DB 0"); otherwise, we
- * will write both that DB's data and the shared stats.
+ * Cluster wide statistics.
+ *
+ * Contains statistics that are not collected per database or per table.
+ * shared_* are the statistics maintained by shared statistics code and
+ * snapshot_* are backend snapshots.
  */
-static List *pending_write_requests = NIL;
-
-/* Signal handler flags */
-static volatile bool need_exit = false;
-static volatile bool got_SIGHUP = false;
+static PgStat_ArchiverStats *shared_archiverStats;
+static PgStat_ArchiverStats *snapshot_archiverStats;
+static PgStat_GlobalStats *shared_globalStats;
+static PgStat_GlobalStats *snapshot_globalStats;
 
 /*
  * Total time charged to functions so far in the current backend.
@@ -279,35 +335,36 @@ static instr_time total_func_time;
  * Local function forward declarations
  * ----------
  */
-#ifdef EXEC_BACKEND
-static pid_t pgstat_forkexec(void);
-#endif
 
-NON_EXEC_STATIC void PgstatCollectorMain(int argc, char *argv[]) pg_attribute_noreturn();
-static void pgstat_exit(SIGNAL_ARGS);
 static void pgstat_beshutdown_hook(int code, Datum arg);
-static void pgstat_sighup_handler(SIGNAL_ARGS);
-
-static PgStat_StatDBEntry *pgstat_get_db_entry(Oid databaseid, bool create);
-static PgStat_StatTabEntry *pgstat_get_tab_entry(PgStat_StatDBEntry *dbentry,
-                     Oid tableoid, bool create);
-static void pgstat_write_statsfiles(bool permanent, bool allDbs);
-static void pgstat_write_db_statsfile(PgStat_StatDBEntry *dbentry, bool permanent);
-static HTAB *pgstat_read_statsfiles(Oid onlydb, bool permanent, bool deep);
-static void pgstat_read_db_statsfile(Oid databaseid, HTAB *tabhash, HTAB *funchash, bool permanent);
-static void backend_read_statsfile(void);
+static PgStat_StatDBEntry *pgstat_get_db_entry(Oid databaseid, int op,
+                                    PgStat_TableLookupState *status);
+static PgStat_StatTabEntry *pgstat_get_tab_entry(dshash_table *table, Oid tableoid, bool create);
+static void pgstat_write_pgStatDBHashfile(PgStat_StatDBEntry *dbentry);
+static void pgstat_read_pgStatDBHashfile(PgStat_StatDBEntry *dbentry);
 static void pgstat_read_current_status(void);
-
-static bool pgstat_write_statsfile_needed(void);
-static bool pgstat_db_requested(Oid databaseid);
-
-static void pgstat_send_tabstat(PgStat_MsgTabstat *tsmsg);
-static void pgstat_send_funcstats(void);
+static bool pgstat_flush_stat(pgstat_flush_stat_context *cxt, bool nowait);
+static bool pgstat_flush_tabstat(pgstat_flush_stat_context *cxt, bool nowait,
+                                 PgStat_TableStatus *entry);
+static bool pgstat_flush_funcstats(pgstat_flush_stat_context *cxt, bool nowait);
+static bool pgstat_flush_miscstats(pgstat_flush_stat_context *cxt, bool nowait);
+static bool pgstat_update_tabentry(dshash_table *tabhash,
+                                   PgStat_TableStatus *stat, bool nowait);
+static void pgstat_update_dbentry(PgStat_StatDBEntry *dbentry,
+                                  PgStat_TableStatus *stat);
 static HTAB *pgstat_collect_oids(Oid catalogid, AttrNumber anum_oid);
 
 static PgStat_TableStatus *get_tabstat_entry(Oid rel_id, bool isshared);
 
 static void pgstat_setup_memcxt(void);
+static void pgstat_flush_recovery_conflict(PgStat_StatDBEntry *dbentry);
+static void pgstat_flush_deadlock(PgStat_StatDBEntry *dbentry);
+static void pgstat_flush_tempfile(PgStat_StatDBEntry *dbentry);
+static HTAB *create_tabstat_hash(void);
+static PgStat_SubXactStatus *get_tabstat_stack_level(int nest_level);
+static void add_tabstat_xact_level(PgStat_TableStatus *pgstat_info, int nest_level);
+static PgStat_StatFuncEntry *pgstat_fetch_stat_funcentry_extended(PgStat_StatDBEntry *dbent, Oid funcid);
+static void pgstat_snapshot_global_stats(void);
 
 static const char *pgstat_get_wait_activity(WaitEventActivity w);
 static const char *pgstat_get_wait_client(WaitEventClient w);
@@ -315,480 +372,134 @@ static const char *pgstat_get_wait_ipc(WaitEventIPC w);
 static const char *pgstat_get_wait_timeout(WaitEventTimeout w);
 static const char *pgstat_get_wait_io(WaitEventIO w);
 
-static void pgstat_setheader(PgStat_MsgHdr *hdr, StatMsgType mtype);
-static void pgstat_send(void *msg, int len);
-
-static void pgstat_recv_inquiry(PgStat_MsgInquiry *msg, int len);
-static void pgstat_recv_tabstat(PgStat_MsgTabstat *msg, int len);
-static void pgstat_recv_tabpurge(PgStat_MsgTabpurge *msg, int len);
-static void pgstat_recv_dropdb(PgStat_MsgDropdb *msg, int len);
-static void pgstat_recv_resetcounter(PgStat_MsgResetcounter *msg, int len);
-static void pgstat_recv_resetsharedcounter(PgStat_MsgResetsharedcounter *msg, int len);
-static void pgstat_recv_resetsinglecounter(PgStat_MsgResetsinglecounter *msg, int len);
-static void pgstat_recv_autovac(PgStat_MsgAutovacStart *msg, int len);
-static void pgstat_recv_vacuum(PgStat_MsgVacuum *msg, int len);
-static void pgstat_recv_analyze(PgStat_MsgAnalyze *msg, int len);
-static void pgstat_recv_archiver(PgStat_MsgArchiver *msg, int len);
-static void pgstat_recv_bgwriter(PgStat_MsgBgWriter *msg, int len);
-static void pgstat_recv_funcstat(PgStat_MsgFuncstat *msg, int len);
-static void pgstat_recv_funcpurge(PgStat_MsgFuncpurge *msg, int len);
-static void pgstat_recv_recoveryconflict(PgStat_MsgRecoveryConflict *msg, int len);
-static void pgstat_recv_deadlock(PgStat_MsgDeadlock *msg, int len);
-static void pgstat_recv_tempfile(PgStat_MsgTempFile *msg, int len);
+/* ------------------------------------------------------------
+ * Local support functions follow
+ * ------------------------------------------------------------
+ */
+static int pin_hashes(PgStat_StatDBEntry *dbentry);
+static void unpin_hashes(PgStat_StatDBEntry *dbentry, int generation);
+static dshash_table *attach_table_hash(PgStat_StatDBEntry *dbent, int gen);
+static dshash_table *attach_function_hash(PgStat_StatDBEntry *dbent, int gen);
+static void reset_dbentry_counters(PgStat_StatDBEntry *dbentry);
 
 /* ------------------------------------------------------------
  * Public functions called from postmaster follow
  * ------------------------------------------------------------
  */
 
-/* ----------
- * pgstat_init() -
- *
- *    Called from postmaster at startup. Create the resources required
- *    by the statistics collector process.  If unable to do so, do not
- *    fail --- better to let the postmaster start with stats collection
- *    disabled.
- * ----------
- */
-void
-pgstat_init(void)
+static void
+pgstat_postmaster_shutdown(int code, Datum arg)
 {
-    ACCEPT_TYPE_ARG3 alen;
-    struct addrinfo *addrs = NULL,
-               *addr,
-                hints;
-    int            ret;
-    fd_set        rset;
-    struct timeval tv;
-    char        test_byte;
-    int            sel_res;
-    int            tries = 0;
-
-#define TESTBYTEVAL ((char) 199)
-
-    /*
-     * This static assertion verifies that we didn't mess up the calculations
-     * involved in selecting maximum payload sizes for our UDP messages.
-     * Because the only consequence of overrunning PGSTAT_MAX_MSG_SIZE would
-     * be silent performance loss from fragmentation, it seems worth having a
-     * compile-time cross-check that we didn't.
-     */
-    StaticAssertStmt(sizeof(PgStat_Msg) <= PGSTAT_MAX_MSG_SIZE,
-                     "maximum stats message size exceeds PGSTAT_MAX_MSG_SIZE");
-
-    /*
-     * Create the UDP socket for sending and receiving statistic messages
-     */
-    hints.ai_flags = AI_PASSIVE;
-    hints.ai_family = AF_UNSPEC;
-    hints.ai_socktype = SOCK_DGRAM;
-    hints.ai_protocol = 0;
-    hints.ai_addrlen = 0;
-    hints.ai_addr = NULL;
-    hints.ai_canonname = NULL;
-    hints.ai_next = NULL;
-    ret = pg_getaddrinfo_all("localhost", NULL, &hints, &addrs);
-    if (ret || !addrs)
-    {
-        ereport(LOG,
-                (errmsg("could not resolve \"localhost\": %s",
-                        gai_strerror(ret))));
-        goto startup_failed;
-    }
-
-    /*
-     * On some platforms, pg_getaddrinfo_all() may return multiple addresses
-     * only one of which will actually work (eg, both IPv6 and IPv4 addresses
-     * when kernel will reject IPv6).  Worse, the failure may occur at the
-     * bind() or perhaps even connect() stage.  So we must loop through the
-     * results till we find a working combination. We will generate LOG
-     * messages, but no error, for bogus combinations.
-     */
-    for (addr = addrs; addr; addr = addr->ai_next)
-    {
-#ifdef HAVE_UNIX_SOCKETS
-        /* Ignore AF_UNIX sockets, if any are returned. */
-        if (addr->ai_family == AF_UNIX)
-            continue;
-#endif
-
-        if (++tries > 1)
-            ereport(LOG,
-                    (errmsg("trying another address for the statistics collector")));
-
-        /*
-         * Create the socket.
-         */
-        if ((pgStatSock = socket(addr->ai_family, SOCK_DGRAM, 0)) == PGINVALID_SOCKET)
-        {
-            ereport(LOG,
-                    (errcode_for_socket_access(),
-                     errmsg("could not create socket for statistics collector: %m")));
-            continue;
-        }
-
-        /*
-         * Bind it to a kernel assigned port on localhost and get the assigned
-         * port via getsockname().
-         */
-        if (bind(pgStatSock, addr->ai_addr, addr->ai_addrlen) < 0)
-        {
-            ereport(LOG,
-                    (errcode_for_socket_access(),
-                     errmsg("could not bind socket for statistics collector: %m")));
-            closesocket(pgStatSock);
-            pgStatSock = PGINVALID_SOCKET;
-            continue;
-        }
-
-        alen = sizeof(pgStatAddr);
-        if (getsockname(pgStatSock, (struct sockaddr *) &pgStatAddr, &alen) < 0)
-        {
-            ereport(LOG,
-                    (errcode_for_socket_access(),
-                     errmsg("could not get address of socket for statistics collector: %m")));
-            closesocket(pgStatSock);
-            pgStatSock = PGINVALID_SOCKET;
-            continue;
-        }
-
-        /*
-         * Connect the socket to its own address.  This saves a few cycles by
-         * not having to respecify the target address on every send. This also
-         * provides a kernel-level check that only packets from this same
-         * address will be received.
-         */
-        if (connect(pgStatSock, (struct sockaddr *) &pgStatAddr, alen) < 0)
-        {
-            ereport(LOG,
-                    (errcode_for_socket_access(),
-                     errmsg("could not connect socket for statistics collector: %m")));
-            closesocket(pgStatSock);
-            pgStatSock = PGINVALID_SOCKET;
-            continue;
-        }
-
-        /*
-         * Try to send and receive a one-byte test message on the socket. This
-         * is to catch situations where the socket can be created but will not
-         * actually pass data (for instance, because kernel packet filtering
-         * rules prevent it).
-         */
-        test_byte = TESTBYTEVAL;
-
-retry1:
-        if (send(pgStatSock, &test_byte, 1, 0) != 1)
-        {
-            if (errno == EINTR)
-                goto retry1;    /* if interrupted, just retry */
-            ereport(LOG,
-                    (errcode_for_socket_access(),
-                     errmsg("could not send test message on socket for statistics collector: %m")));
-            closesocket(pgStatSock);
-            pgStatSock = PGINVALID_SOCKET;
-            continue;
-        }
-
-        /*
-         * There could possibly be a little delay before the message can be
-         * received.  We arbitrarily allow up to half a second before deciding
-         * it's broken.
-         */
-        for (;;)                /* need a loop to handle EINTR */
-        {
-            FD_ZERO(&rset);
-            FD_SET(pgStatSock, &rset);
-
-            tv.tv_sec = 0;
-            tv.tv_usec = 500000;
-            sel_res = select(pgStatSock + 1, &rset, NULL, NULL, &tv);
-            if (sel_res >= 0 || errno != EINTR)
-                break;
-        }
-        if (sel_res < 0)
-        {
-            ereport(LOG,
-                    (errcode_for_socket_access(),
-                     errmsg("select() failed in statistics collector: %m")));
-            closesocket(pgStatSock);
-            pgStatSock = PGINVALID_SOCKET;
-            continue;
-        }
-        if (sel_res == 0 || !FD_ISSET(pgStatSock, &rset))
-        {
-            /*
-             * This is the case we actually think is likely, so take pains to
-             * give a specific message for it.
-             *
-             * errno will not be set meaningfully here, so don't use it.
-             */
-            ereport(LOG,
-                    (errcode(ERRCODE_CONNECTION_FAILURE),
-                     errmsg("test message did not get through on socket for statistics collector")));
-            closesocket(pgStatSock);
-            pgStatSock = PGINVALID_SOCKET;
-            continue;
-        }
-
-        test_byte++;            /* just make sure variable is changed */
-
-retry2:
-        if (recv(pgStatSock, &test_byte, 1, 0) != 1)
-        {
-            if (errno == EINTR)
-                goto retry2;    /* if interrupted, just retry */
-            ereport(LOG,
-                    (errcode_for_socket_access(),
-                     errmsg("could not receive test message on socket for statistics collector: %m")));
-            closesocket(pgStatSock);
-            pgStatSock = PGINVALID_SOCKET;
-            continue;
-        }
-
-        if (test_byte != TESTBYTEVAL)    /* strictly paranoia ... */
-        {
-            ereport(LOG,
-                    (errcode(ERRCODE_INTERNAL_ERROR),
-                     errmsg("incorrect test message transmission on socket for statistics collector")));
-            closesocket(pgStatSock);
-            pgStatSock = PGINVALID_SOCKET;
-            continue;
-        }
-
-        /* If we get here, we have a working socket */
-        break;
-    }
-
-    /* Did we find a working address? */
-    if (!addr || pgStatSock == PGINVALID_SOCKET)
-        goto startup_failed;
-
-    /*
-     * Set the socket to non-blocking IO.  This ensures that if the collector
-     * falls behind, statistics messages will be discarded; backends won't
-     * block waiting to send messages to the collector.
-     */
-    if (!pg_set_noblock(pgStatSock))
-    {
-        ereport(LOG,
-                (errcode_for_socket_access(),
-                 errmsg("could not set statistics collector socket to nonblocking mode: %m")));
-        goto startup_failed;
-    }
-
-    /*
-     * Try to ensure that the socket's receive buffer is at least
-     * PGSTAT_MIN_RCVBUF bytes, so that it won't easily overflow and lose
-     * data.  Use of UDP protocol means that we are willing to lose data under
-     * heavy load, but we don't want it to happen just because of ridiculously
-     * small default buffer sizes (such as 8KB on older Windows versions).
-     */
-    {
-        int            old_rcvbuf;
-        int            new_rcvbuf;
-        ACCEPT_TYPE_ARG3 rcvbufsize = sizeof(old_rcvbuf);
-
-        if (getsockopt(pgStatSock, SOL_SOCKET, SO_RCVBUF,
-                       (char *) &old_rcvbuf, &rcvbufsize) < 0)
-        {
-            elog(LOG, "getsockopt(SO_RCVBUF) failed: %m");
-            /* if we can't get existing size, always try to set it */
-            old_rcvbuf = 0;
-        }
-
-        new_rcvbuf = PGSTAT_MIN_RCVBUF;
-        if (old_rcvbuf < new_rcvbuf)
-        {
-            if (setsockopt(pgStatSock, SOL_SOCKET, SO_RCVBUF,
-                           (char *) &new_rcvbuf, sizeof(new_rcvbuf)) < 0)
-                elog(LOG, "setsockopt(SO_RCVBUF) failed: %m");
-        }
-    }
-
-    pg_freeaddrinfo_all(hints.ai_family, addrs);
-
-    return;
-
-startup_failed:
-    ereport(LOG,
-            (errmsg("disabling statistics collector for lack of working socket")));
-
-    if (addrs)
-        pg_freeaddrinfo_all(hints.ai_family, addrs);
-
-    if (pgStatSock != PGINVALID_SOCKET)
-        closesocket(pgStatSock);
-    pgStatSock = PGINVALID_SOCKET;
-
-    /*
-     * Adjust GUC variables to suppress useless activity, and for debugging
-     * purposes (seeing track_counts off is a clue that we failed here). We
-     * use PGC_S_OVERRIDE because there is no point in trying to turn it back
-     * on from postgresql.conf without a restart.
-     */
-    SetConfigOption("track_counts", "off", PGC_INTERNAL, PGC_S_OVERRIDE);
+    /* trash the stats on crash */
+    if (code == 0)
+        pgstat_write_statsfiles();
 }
 
-/*
- * subroutine for pgstat_reset_all
+Size
+StatsShmemSize(void)
+{
+    return sizeof(StatsShmemStruct);
+}
+
+void
+StatsShmemInit(void)
+{
+    bool    found;
+
+    StatsShmem = (StatsShmemStruct *)
+        ShmemInitStruct("Stats area", StatsShmemSize(),
+                        &found);
+    if (!IsUnderPostmaster)
+    {
+        Assert(!found);
+
+        StatsShmem->stats_dsa_handle = DSM_HANDLE_INVALID;
+
+        /* Load saved data if any */
+        pgstat_read_statsfiles();
+
+        /* need to be called before dsm shutodwn */
+        before_shmem_exit(pgstat_postmaster_shutdown, (Datum) 0);
+    }
+
+    LWLockInitialize(StatsLock, LWTRANCHE_STATS);
+}
+
+/* ----------
+ * pgstat_create_shared_stats() -
+ *
+ *    create shared stats memory
+ * ----------
  */
 static void
-pgstat_reset_remove_files(const char *directory)
+pgstat_create_shared_stats(void)
 {
-    DIR           *dir;
-    struct dirent *entry;
-    char        fname[MAXPGPATH * 2];
+    MemoryContext oldcontext;
 
-    dir = AllocateDir(directory);
-    while ((entry = ReadDir(dir, directory)) != NULL)
-    {
-        int            nchars;
-        Oid            tmp_oid;
+    Assert(StatsShmem->stats_dsa_handle == DSM_HANDLE_INVALID);
 
-        /*
-         * Skip directory entries that don't match the file names we write.
-         * See get_dbstat_filename for the database-specific pattern.
-         */
-        if (strncmp(entry->d_name, "global.", 7) == 0)
-            nchars = 7;
-        else
-        {
-            nchars = 0;
-            (void) sscanf(entry->d_name, "db_%u.%n",
-                          &tmp_oid, &nchars);
-            if (nchars <= 0)
-                continue;
-            /* %u allows leading whitespace, so reject that */
-            if (strchr("0123456789", entry->d_name[3]) == NULL)
-                continue;
-        }
+    /* lives for the lifetime of the process */
+    oldcontext = MemoryContextSwitchTo(TopMemoryContext);
+    area = dsa_create(LWTRANCHE_STATS);
+    dsa_pin_mapping(area);
 
-        if (strcmp(entry->d_name + nchars, "tmp") != 0 &&
-            strcmp(entry->d_name + nchars, "stat") != 0)
-            continue;
+    /* create the database hash */
+    pgStatDBHash = dshash_create(area, &dsh_dbparams, 0);
 
-        snprintf(fname, sizeof(fname), "%s/%s", directory,
-                 entry->d_name);
-        unlink(fname);
-    }
-    FreeDir(dir);
+    /* create shared area and write bootstrap information */
+    StatsShmem->stats_dsa_handle = dsa_get_handle(area);
+    StatsShmem->global_stats =
+        dsa_allocate0(area, sizeof(PgStat_GlobalStats));
+    StatsShmem->archiver_stats =
+        dsa_allocate0(area, sizeof(PgStat_ArchiverStats));
+    StatsShmem->db_hash_handle =
+        dshash_get_hash_table_handle(pgStatDBHash);
+    StatsShmem->last_update = 0;
+
+    /* initial connect to the memory */
+    MemoryContextSwitchTo(pgSharedStatsContext);
+    pgStatDBEntrySnapshot = NULL;
+    shared_globalStats = (PgStat_GlobalStats *)
+        dsa_get_address(area, StatsShmem->global_stats);
+    shared_archiverStats = (PgStat_ArchiverStats *)
+        dsa_get_address(area, StatsShmem->archiver_stats);
+    MemoryContextSwitchTo(oldcontext);
 }
 
 /*
  * pgstat_reset_all() -
  *
- * Remove the stats files.  This is currently used only if WAL
- * recovery is needed after a crash.
+ * Clear on-memory counters.  This is currently used only if WAL recovery is
+ * needed after a crash.
  */
 void
 pgstat_reset_all(void)
 {
-    pgstat_reset_remove_files(pgstat_stat_directory);
-    pgstat_reset_remove_files(PGSTAT_STAT_PERMANENT_DIRECTORY);
-}
+    dshash_seq_status dshstat;
+    PgStat_StatDBEntry           *dbentry;
 
-#ifdef EXEC_BACKEND
+    Assert (pgStatDBHash);
 
-/*
- * pgstat_forkexec() -
- *
- * Format up the arglist for, then fork and exec, statistics collector process
- */
-static pid_t
-pgstat_forkexec(void)
-{
-    char       *av[10];
-    int            ac = 0;
-
-    av[ac++] = "postgres";
-    av[ac++] = "--forkcol";
-    av[ac++] = NULL;            /* filled in by postmaster_forkexec */
-
-    av[ac] = NULL;
-    Assert(ac < lengthof(av));
-
-    return postmaster_forkexec(ac, av);
-}
-#endif                            /* EXEC_BACKEND */
-
-
-/*
- * pgstat_start() -
- *
- *    Called from postmaster at startup or after an existing collector
- *    died.  Attempt to fire up a fresh statistics collector.
- *
- *    Returns PID of child process, or 0 if fail.
- *
- *    Note: if fail, we will be called again from the postmaster main loop.
- */
-int
-pgstat_start(void)
-{
-    time_t        curtime;
-    pid_t        pgStatPid;
-
-    /*
-     * Check that the socket is there, else pgstat_init failed and we can do
-     * nothing useful.
-     */
-    if (pgStatSock == PGINVALID_SOCKET)
-        return 0;
-
-    /*
-     * Do nothing if too soon since last collector start.  This is a safety
-     * valve to protect against continuous respawn attempts if the collector
-     * is dying immediately at launch.  Note that since we will be re-called
-     * from the postmaster main loop, we will get another chance later.
-     */
-    curtime = time(NULL);
-    if ((unsigned int) (curtime - last_pgstat_start_time) <
-        (unsigned int) PGSTAT_RESTART_INTERVAL)
-        return 0;
-    last_pgstat_start_time = curtime;
-
-    /*
-     * Okay, fork off the collector.
-     */
-#ifdef EXEC_BACKEND
-    switch ((pgStatPid = pgstat_forkexec()))
-#else
-    switch ((pgStatPid = fork_process()))
-#endif
+    dshash_seq_init(&dshstat, pgStatDBHash, false, true);
+    while ((dbentry = (PgStat_StatDBEntry *) dshash_seq_next(&dshstat)) != NULL)
     {
-        case -1:
-            ereport(LOG,
-                    (errmsg("could not fork statistics collector: %m")));
-            return 0;
-
-#ifndef EXEC_BACKEND
-        case 0:
-            /* in postmaster child ... */
-            InitPostmasterChild();
-
-            /* Close the postmaster's sockets */
-            ClosePostmasterPorts(false);
-
-            /* Drop our connection to postmaster's shared memory, as well */
-            dsm_detach_all();
-            PGSharedMemoryDetach();
-
-            PgstatCollectorMain(0, NULL);
-            break;
-#endif
-
-        default:
-            return (int) pgStatPid;
+        /*
+         * Reset database-level stats, too.  This creates empty hash tables
+         * for tables and functions.
+         */
+        reset_dbentry_counters(dbentry);
+        dshash_release_lock(pgStatDBHash, dbentry);
     }
 
-    /* shouldn't get here */
-    return 0;
-}
-
-void
-allow_immediate_pgstat_restart(void)
-{
-    last_pgstat_start_time = 0;
+    /*
+     * Reset global counters
+     */
+    LWLockAcquire(StatsLock, LW_EXCLUSIVE);
+    MemSet(shared_globalStats, 0, sizeof(*shared_globalStats));
+    MemSet(shared_archiverStats, 0, sizeof(*shared_archiverStats));
+    shared_globalStats->stat_reset_timestamp =
+        shared_archiverStats->stat_reset_timestamp = GetCurrentTimestamp();
+    LWLockRelease(StatsLock);
 }
 
 /* ------------------------------------------------------------
@@ -796,75 +507,257 @@ allow_immediate_pgstat_restart(void)
  *------------------------------------------------------------
  */
 
-
 /* ----------
- * pgstat_report_stat() -
+ * pgstat_flush_stat() -
  *
  *    Must be called by processes that performs DML: tcop/postgres.c, logical
- *    receiver processes, SPI worker, etc. to send the so far collected
- *    per-table and function usage statistics to the collector.  Note that this
- *    is called only when not within a transaction, so it is fair to use
+ *    receiver processes, SPI worker, etc. to apply the so far collected
+ *    per-table and function usage statistics to the shared statistics hashes.
+ *
+ *    This requires taking some locks on the shared statistics hashes and some
+ *    of updates may be postponed on lock failure. Such postponed updates are
+ *    retried in later call of this function and finally cleaned up by calling
+ *    this function with force = true or PGSTAT_STAT_MAX_INTERVAL milliseconds
+ *    has elapsed since last cleanup. On the other hand updates by regular
+ *    backends happen with the interval not shorter than
+ *    PGSTAT_STAT_MIN_INTERVAL when force = false.
+ *
+ *    Returns the time until the next update time in milliseconds.
+ *
+ *    Note that this is called only out of a transaction, so it is fair to use
  *    transaction stop time as an approximation of current time.
- * ----------
+ *    ----------
  */
-void
+long
 pgstat_report_stat(bool force)
 {
-    /* we assume this inits to all zeroes: */
-    static const PgStat_TableCounts all_zeroes;
-    static TimestampTz last_report = 0;
-
+    static TimestampTz last_flush = 0;
+    static TimestampTz pending_since = 0;
     TimestampTz now;
-    PgStat_MsgTabstat regular_msg;
-    PgStat_MsgTabstat shared_msg;
-    TabStatusArray *tsa;
-    int            i;
+    pgstat_flush_stat_context cxt = {0};
+    bool        have_other_stats = false;
+    bool        pending_stats = false;
+    long        elapsed;
+    long        secs;
+    int            usecs;
+
+    /* Do we have anything to flush? */
+    if (have_recovery_conflicts || n_deadlocks != 0 || n_tmpfiles != 0)
+        have_other_stats = true;
 
     /* Don't expend a clock check if nothing to do */
     if ((pgStatTabList == NULL || pgStatTabList->tsa_used == 0) &&
         pgStatXactCommit == 0 && pgStatXactRollback == 0 &&
-        !have_function_stats)
-        return;
+        !have_other_stats && !have_function_stats)
+        return 0;
+
+    now = GetCurrentTransactionStopTimestamp();
+
+    if (!force)
+    {
+        /*
+         * Don't flush stats unless it's been at least
+         * PGSTAT_STAT_MIN_INTERVAL msec since the last flush.  Returns time
+         * to wait in the case.
+         */
+        TimestampDifference(last_flush, now, &secs, &usecs);
+        elapsed = secs * 1000 + usecs /1000;
+
+        if(elapsed < PGSTAT_STAT_MIN_INTERVAL)
+        {
+            if (pending_since == 0)
+                pending_since = now;
+
+            return PGSTAT_STAT_MIN_INTERVAL - elapsed;
+        }
+
+
+        /*
+         * Don't keep pending stats for longer than PGSTAT_STAT_MAX_INTERVAL.
+         */
+        if (pending_since > 0)
+        {
+            TimestampDifference(pending_since, now, &secs, &usecs);
+            elapsed = secs * 1000 + usecs /1000;
+
+            if(elapsed > PGSTAT_STAT_MAX_INTERVAL)
+                force = true;
+        }
+    }
+
+    /* It's the time to flush */
+    last_flush = now;
+
+    /* Flush out table stats */
+    if (pgStatTabList != NULL && !pgstat_flush_stat(&cxt, !force))
+        pending_stats = true;
+
+    /* Flush out function stats */
+    if (pgStatFunctions != NULL && !pgstat_flush_funcstats(&cxt, !force))
+        pending_stats = true;
+
+    /* Flush out miscellaneous stats */
+    if (have_other_stats && !pgstat_flush_miscstats(&cxt, !force))
+        pending_stats = true;
+
+    /*  Unpin dbentry if pinned */
+    if (cxt.mydbentry)
+        unpin_hashes(cxt.mydbentry, cxt.mygeneration);
+
+    /* Publish the last flush time */
+    LWLockAcquire(StatsLock, LW_EXCLUSIVE);
+    if (StatsShmem->last_update < last_flush)
+        StatsShmem->last_update = last_flush;
+    LWLockRelease(StatsLock);
+
+    /* record how long we keep pending stats */
+    if (pending_stats)
+    {
+        if (pending_since == 0)
+            pending_since = now;
+        return PGSTAT_STAT_RETRY_INTERVAL;
+    }
+
+    pending_since = 0;
+
+    return 0;
+}
+
+/* -------
+ * Subroutines for pgstat_flush_stat.
+ * -------
+ */
+
+/*
+ * snapshot_statentry() - Find an entry from source dshash with cache.
+ *
+ * Returns the entry for key or NULL if not found.
+ *
+ * Returned entries are consistent during the current transaction or
+ * pgstat_clear_snapshot() is called.
+ *
+ * *cxt->hash points to a HTAB* variable to store the hash for local cache. New
+ * one is created if it is not yet created.
+ *
+ * *cxt->dshash points to dshash_table* variable to store the attached
+ * dshash. *cxt->dsh_handle is * attached if not yet attached.
+ */
+static void *
+snapshot_statentry(pgstat_snapshot_cxt *cxt, Oid key)
+{
+    char *lentry = NULL;
+    size_t keysize = cxt->dsh_params->key_size;
+    size_t dsh_entrysize = cxt->dsh_params->entry_size;
+    bool found;
+    bool *negative;
+
+    /* caches the result entry */
 
     /*
-     * Don't send a message unless it's been at least PGSTAT_STAT_INTERVAL
-     * msec since we last sent one, or the caller wants to force stats out.
+     * Create new hash with arbitrary initial entries since we don't know how
+     * this hash will grow. The boolean put at the end of the entry is
+     * negative flag.
      */
-    now = GetCurrentTransactionStopTimestamp();
-    if (!force &&
-        !TimestampDifferenceExceeds(last_report, now, PGSTAT_STAT_INTERVAL))
-        return;
-    last_report = now;
+    if (!*cxt->hash)
+    {
+        HASHCTL ctl;
+
+        /* Create the hash in the stats context */
+        ctl.keysize        = keysize;
+        ctl.entrysize    = cxt->hash_entsize + sizeof(bool);
+        ctl.hcxt        = pgStatSnapshotContext;
+        *cxt->hash = hash_create(cxt->hash_name, 32, &ctl,
+                                 HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+    }
+
+    lentry = hash_search(*cxt->hash, &key, HASH_ENTER, &found);
+
+    negative = (bool *) (lentry + cxt->hash_entsize);
+
+    if (!found)
+    {
+        /* not found in local cache, search shared hash */
+
+        void *sentry;
+
+        /* attach shared hash if not given, leave it alone for later use */
+        if (!*cxt->dshash)
+        {
+            MemoryContext oldcxt;
+
+            if (cxt->dsh_handle == DSM_HANDLE_INVALID)
+                return NULL;
+
+            oldcxt = MemoryContextSwitchTo(pgStatSnapshotContext);
+            *cxt->dshash =
+                dshash_attach(area, cxt->dsh_params, cxt->dsh_handle, NULL);
+            MemoryContextSwitchTo(oldcxt);
+        }
+
+        sentry = dshash_find(*cxt->dshash, &key, false);
+
+        if (sentry)
+        {
+            /* found copy it */
+            memcpy(lentry, sentry, dsh_entrysize);
+            dshash_release_lock(*cxt->dshash, sentry);
+
+            /* then zero out the additional space */
+            if (dsh_entrysize < cxt->hash_entsize)
+                MemSet(lentry + dsh_entrysize, 0,
+                       cxt->hash_entsize - dsh_entrysize);
+        }
+
+        *negative = !sentry;
+    }
+
+    if (*negative)
+        return NULL;
+
+    return (void *) lentry;
+}
+
+/*
+ * pgstat_flush_stat: Flushes table stats out to shared statistics.
+ *
+ *  If nowait is true, returns with false if required lock was not acquired
+ *  immediately. In the case, infos of some tables may be left alone in TSA to
+ *  wait for the next chance. cxt holds some dshash related values that we
+ *  want to keep during the shared stats update.  Returns true if no stats
+ *  info remains. Caller must detach dshashes stored in cxt after use.
+ *
+ *  Returns true if all entries are flushed.
+ */
+static bool
+pgstat_flush_stat(pgstat_flush_stat_context *cxt, bool nowait)
+{
+    static const PgStat_TableCounts all_zeroes;
+    TabStatusArray *tsa;
+    HTAB           *new_tsa_hash = NULL;
+    TabStatusArray *dest_tsa = pgStatTabList;
+    int                dest_elem = 0;
+    int                i;
+
+    /* nothing to do, just return  */
+    if (pgStatTabHash == NULL)
+        return true;
 
     /*
      * Destroy pgStatTabHash before we start invalidating PgStat_TableEntry
-     * entries it points to.  (Should we fail partway through the loop below,
-     * it's okay to have removed the hashtable already --- the only
-     * consequence is we'd get multiple entries for the same table in the
-     * pgStatTabList, and that's safe.)
+     * entries it points to. We recreate it if is needed.
      */
-    if (pgStatTabHash)
-        hash_destroy(pgStatTabHash);
+    hash_destroy(pgStatTabHash);
     pgStatTabHash = NULL;
 
     /*
      * Scan through the TabStatusArray struct(s) to find tables that actually
-     * have counts, and build messages to send.  We have to separate shared
-     * relations from regular ones because the databaseid field in the message
-     * header has to depend on that.
+     * have counts, and try flushing it out to shared statistics.
      */
-    regular_msg.m_databaseid = MyDatabaseId;
-    shared_msg.m_databaseid = InvalidOid;
-    regular_msg.m_nentries = 0;
-    shared_msg.m_nentries = 0;
-
     for (tsa = pgStatTabList; tsa != NULL; tsa = tsa->tsa_next)
     {
         for (i = 0; i < tsa->tsa_used; i++)
         {
             PgStat_TableStatus *entry = &tsa->tsa_entries[i];
-            PgStat_MsgTabstat *this_msg;
-            PgStat_TableEntry *this_ent;
 
             /* Shouldn't have any pending transaction-dependent counts */
             Assert(entry->trans == NULL);
@@ -877,178 +770,344 @@ pgstat_report_stat(bool force)
                        sizeof(PgStat_TableCounts)) == 0)
                 continue;
 
-            /*
-             * OK, insert data into the appropriate message, and send if full.
-             */
-            this_msg = entry->t_shared ? &shared_msg : ®ular_msg;
-            this_ent = &this_msg->m_entry[this_msg->m_nentries];
-            this_ent->t_id = entry->t_id;
-            memcpy(&this_ent->t_counts, &entry->t_counts,
-                   sizeof(PgStat_TableCounts));
-            if (++this_msg->m_nentries >= PGSTAT_NUM_TABENTRIES)
+            /* try to apply the tab stats */
+            if (!pgstat_flush_tabstat(cxt, nowait, entry))
             {
-                pgstat_send_tabstat(this_msg);
-                this_msg->m_nentries = 0;
+                /*
+                 * Failed. Leave it alone filling at the beginning in TSA.
+                 */
+                TabStatHashEntry *hash_entry;
+                bool found;
+
+                if (new_tsa_hash == NULL)
+                    new_tsa_hash = create_tabstat_hash();
+
+                /* Create hash entry for this entry */
+                hash_entry = hash_search(new_tsa_hash, &entry->t_id,
+                                         HASH_ENTER, &found);
+                Assert(!found);
+
+                /*
+                 * Move insertion pointer to the next segment. There must be
+                 * enough space segments since we are just leaving some of the
+                 * current elements.
+                 */
+                if (dest_elem >= TABSTAT_QUANTUM)
+                {
+                    Assert(dest_tsa->tsa_next != NULL);
+                    dest_tsa = dest_tsa->tsa_next;
+                    dest_elem = 0;
+                }
+
+                /* Move the entry if needed */
+                if (tsa != dest_tsa || i != dest_elem)
+                {
+                    PgStat_TableStatus *new_entry;
+                    new_entry = &dest_tsa->tsa_entries[dest_elem];
+                    *new_entry = *entry;
+                    entry = new_entry;
+                }
+
+                hash_entry->tsa_entry = entry;
+                dest_elem++;
             }
         }
-        /* zero out TableStatus structs after use */
-        MemSet(tsa->tsa_entries, 0,
-               tsa->tsa_used * sizeof(PgStat_TableStatus));
-        tsa->tsa_used = 0;
     }
 
-    /*
-     * Send partial messages.  Make sure that any pending xact commit/abort
-     * gets counted, even if there are no table stats to send.
-     */
-    if (regular_msg.m_nentries > 0 ||
-        pgStatXactCommit > 0 || pgStatXactRollback > 0)
-        pgstat_send_tabstat(®ular_msg);
-    if (shared_msg.m_nentries > 0)
-        pgstat_send_tabstat(&shared_msg);
+    /* zero out unused area of TableStatus */
+    dest_tsa->tsa_used = dest_elem;
+    MemSet(&dest_tsa->tsa_entries[dest_elem], 0,
+           (TABSTAT_QUANTUM - dest_elem) * sizeof(PgStat_TableStatus));
+    while (dest_tsa->tsa_next)
+    {
+        dest_tsa = dest_tsa->tsa_next;
+        MemSet(dest_tsa->tsa_entries, 0,
+               dest_tsa->tsa_used * sizeof(PgStat_TableStatus));
+        dest_tsa->tsa_used = 0;
+    }
 
-    /* Now, send function statistics */
-    pgstat_send_funcstats();
+    /* and set the new TSA hash if any */
+    pgStatTabHash = new_tsa_hash;
+
+    /*
+     * We no longer need shared database and table entries , but still may
+     * use that for my database.
+     */
+    if (cxt->shdb_tabhash)
+    {
+        dshash_detach(cxt->shdb_tabhash);
+        unpin_hashes(cxt->shdbentry, cxt->shgeneration);
+        cxt->shdb_tabhash = NULL;
+        cxt->shdbentry = NULL;
+    }
+
+    return pgStatTabHash == NULL;
 }
 
+
 /*
- * Subroutine for pgstat_report_stat: finish and send a tabstat message
+ * pgstat_flush_tabstat: Flushes a table stats entry.
+ *
+ *  If nowait is true, returns false on lock failure.  Dshashes for table and
+ *  function stats are kept attached in ctx. The caller must detach them after
+ *  use.
+ *
+ *  Returns true if the entry is flushed.
  */
-static void
-pgstat_send_tabstat(PgStat_MsgTabstat *tsmsg)
+bool
+pgstat_flush_tabstat(pgstat_flush_stat_context *cxt, bool nowait,
+                     PgStat_TableStatus *entry)
 {
-    int            n;
-    int            len;
+    Oid        dboid = entry->t_shared ? InvalidOid : MyDatabaseId;
+    int        table_mode = PGSTAT_FETCH_EXCLUSIVE;
+    bool    updated = false;
+    dshash_table *tabhash;
+    PgStat_StatDBEntry *dbent;
+    int        generation;
 
-    /* It's unlikely we'd get here with no socket, but maybe not impossible */
-    if (pgStatSock == PGINVALID_SOCKET)
-        return;
+    if (nowait)
+        table_mode |= PGSTAT_FETCH_NOWAIT;
 
-    /*
-     * Report and reset accumulated xact commit/rollback and I/O timings
-     * whenever we send a normal tabstat message
-     */
-    if (OidIsValid(tsmsg->m_databaseid))
+    /* Attach the required table hash if not yet. */
+    if ((entry->t_shared ? cxt->shdb_tabhash : cxt->mydb_tabhash) == NULL)
     {
-        tsmsg->m_xact_commit = pgStatXactCommit;
-        tsmsg->m_xact_rollback = pgStatXactRollback;
-        tsmsg->m_block_read_time = pgStatBlockReadTime;
-        tsmsg->m_block_write_time = pgStatBlockWriteTime;
-        pgStatXactCommit = 0;
-        pgStatXactRollback = 0;
-        pgStatBlockReadTime = 0;
-        pgStatBlockWriteTime = 0;
+        /* We don't have corresponding dbentry here */
+        dbent = pgstat_get_db_entry(dboid, table_mode, NULL);
+        if (!dbent)
+            return false;
+
+        /*
+         * We don't hold dshash-lock on dbentries, since the dbentries cannot
+         * be dropped meanwhile.
+         */
+        generation = pin_hashes(dbent);
+        tabhash = attach_table_hash(dbent, generation);
+
+        if (entry->t_shared)
+        {
+            cxt->shgeneration = generation;
+            cxt->shdbentry = dbent;
+            cxt->shdb_tabhash = tabhash;
+        }
+        else
+        {
+            cxt->mygeneration = generation;
+            cxt->mydbentry = dbent;
+            cxt->mydb_tabhash = tabhash;
+
+            /*
+             * We attach mydb tabhash once per flushing. This is the chance to
+             * update database-wide stats
+             */
+            LWLockAcquire(&dbent->lock, LW_EXCLUSIVE);
+            dbent->n_xact_commit += pgStatXactCommit;
+            dbent->n_xact_rollback += pgStatXactRollback;
+            dbent->n_block_read_time += pgStatBlockReadTime;
+            dbent->n_block_write_time += pgStatBlockWriteTime;
+            LWLockRelease(&dbent->lock);
+            pgStatXactCommit = 0;
+            pgStatXactRollback = 0;
+            pgStatBlockReadTime = 0;
+            pgStatBlockWriteTime = 0;
+        }
+    }
+    else if (entry->t_shared)
+    {
+        dbent = cxt->shdbentry;
+        tabhash = cxt->shdb_tabhash;
     }
     else
     {
-        tsmsg->m_xact_commit = 0;
-        tsmsg->m_xact_rollback = 0;
-        tsmsg->m_block_read_time = 0;
-        tsmsg->m_block_write_time = 0;
+        dbent = cxt->mydbentry;
+        tabhash = cxt->mydb_tabhash;
     }
 
-    n = tsmsg->m_nentries;
-    len = offsetof(PgStat_MsgTabstat, m_entry[0]) +
-        n * sizeof(PgStat_TableEntry);
 
-    pgstat_setheader(&tsmsg->m_hdr, PGSTAT_MTYPE_TABSTAT);
-    pgstat_send(tsmsg, len);
+    /*
+     * dbentry is always available here, so try flush table stats first, then
+     * database stats.
+     */
+    if (pgstat_update_tabentry(tabhash, entry, nowait))
+    {
+        pgstat_update_dbentry(dbent, entry);
+        updated = true;
+    }
+
+    return updated;
 }
 
 /*
- * Subroutine for pgstat_report_stat: populate and send a function stat message
+ * pgstat_flush_funcstats: Flushes function stats.
+ *
+ *  If nowait is true, returns false on lock failure and leave some of the
+ *  entries alone in the local hash.
+ *
+ *  Returns true if all entries are flushed.
  */
-static void
-pgstat_send_funcstats(void)
+static bool
+pgstat_flush_funcstats(pgstat_flush_stat_context *cxt, bool nowait)
 {
     /* we assume this inits to all zeroes: */
     static const PgStat_FunctionCounts all_zeroes;
-
-    PgStat_MsgFuncstat msg;
-    PgStat_BackendFunctionEntry *entry;
+    dshash_table   *funchash;
     HASH_SEQ_STATUS fstat;
+    PgStat_BackendFunctionEntry *bestat;
 
+    /* nothing to do, just return  */
     if (pgStatFunctions == NULL)
-        return;
+        return true;
 
-    pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_FUNCSTAT);
-    msg.m_databaseid = MyDatabaseId;
-    msg.m_nentries = 0;
-
-    hash_seq_init(&fstat, pgStatFunctions);
-    while ((entry = (PgStat_BackendFunctionEntry *) hash_seq_search(&fstat)) != NULL)
+    /* get dbentry into cxt if not yet.  */
+    if (cxt->mydbentry == NULL)
     {
-        PgStat_FunctionEntry *m_ent;
+        int op = PGSTAT_FETCH_EXCLUSIVE;
 
-        /* Skip it if no counts accumulated since last time */
-        if (memcmp(&entry->f_counts, &all_zeroes,
+        if (nowait)
+            op |= PGSTAT_FETCH_NOWAIT;
+
+        cxt->mydbentry = pgstat_get_db_entry(MyDatabaseId, op, NULL);
+
+        if (cxt->mydbentry == NULL)
+            return false;
+
+        cxt->mygeneration = pin_hashes(cxt->mydbentry);
+    }
+
+    funchash = attach_function_hash(cxt->mydbentry, cxt->mygeneration);
+    if (funchash == NULL)
+        return false;
+
+    have_function_stats = false;
+
+    /*
+     * Scan through the pgStatFunctions to find functions that actually have
+     * counts, and try flushing it out to shared statistics.
+     */
+    hash_seq_init(&fstat, pgStatFunctions);
+    while ((bestat = (PgStat_BackendFunctionEntry *) hash_seq_search(&fstat)) != NULL)
+    {
+        bool found;
+        PgStat_StatFuncEntry *funcent = NULL;
+
+        /* Skip it if no counts accumulated for it so far */
+        if (memcmp(&bestat->f_counts, &all_zeroes,
                    sizeof(PgStat_FunctionCounts)) == 0)
             continue;
 
-        /* need to convert format of time accumulators */
-        m_ent = &msg.m_entry[msg.m_nentries];
-        m_ent->f_id = entry->f_id;
-        m_ent->f_numcalls = entry->f_counts.f_numcalls;
-        m_ent->f_total_time = INSTR_TIME_GET_MICROSEC(entry->f_counts.f_total_time);
-        m_ent->f_self_time = INSTR_TIME_GET_MICROSEC(entry->f_counts.f_self_time);
+        funcent = (PgStat_StatFuncEntry *)
+            dshash_find_or_insert_extended(funchash, (void *) &(bestat->f_id),
+                                           &found, nowait);
 
-        if (++msg.m_nentries >= PGSTAT_NUM_FUNCENTRIES)
+        /*
+         * We couldn't acquire lock on the required entry. Leave the local
+         * entry alone.
+         */
+        if (!funcent)
         {
-            pgstat_send(&msg, offsetof(PgStat_MsgFuncstat, m_entry[0]) +
-                        msg.m_nentries * sizeof(PgStat_FunctionEntry));
-            msg.m_nentries = 0;
+            have_function_stats = true;
+            continue;
         }
 
-        /* reset the entry's counts */
-        MemSet(&entry->f_counts, 0, sizeof(PgStat_FunctionCounts));
+        /* Initialize if it's new, or add to it. */
+        if (!found)
+        {
+            funcent->functionid = bestat->f_id;
+            funcent->f_numcalls = bestat->f_counts.f_numcalls;
+            funcent->f_total_time =
+                INSTR_TIME_GET_MICROSEC(bestat->f_counts.f_total_time);
+            funcent->f_self_time =
+                INSTR_TIME_GET_MICROSEC(bestat->f_counts.f_self_time);
+        }
+        else
+        {
+            funcent->f_numcalls += bestat->f_counts.f_numcalls;
+            funcent->f_total_time +=
+                INSTR_TIME_GET_MICROSEC(bestat->f_counts.f_total_time);
+            funcent->f_self_time +=
+                INSTR_TIME_GET_MICROSEC(bestat->f_counts.f_self_time);
+        }
+        dshash_release_lock(funchash, funcent);
+
+        /* reset used counts */
+        MemSet(&bestat->f_counts, 0, sizeof(PgStat_FunctionCounts));
     }
 
-    if (msg.m_nentries > 0)
-        pgstat_send(&msg, offsetof(PgStat_MsgFuncstat, m_entry[0]) +
-                    msg.m_nentries * sizeof(PgStat_FunctionEntry));
-
-    have_function_stats = false;
+    return !have_function_stats;
 }
 
+/*
+ * pgstat_flush_miscstats: Flushes out miscellaneous stats.
+ *
+ *  If nowait is true, returns with false on lock failure on dbentry.
+ *
+ *  Returns true if all the miscellaneous stats are flushed out.
+ */
+static bool
+pgstat_flush_miscstats(pgstat_flush_stat_context *cxt, bool nowait)
+{
+    /* get dbentry if not yet.  */
+    if (cxt->mydbentry == NULL)
+    {
+        int op = PGSTAT_FETCH_EXCLUSIVE;
+        if (nowait)
+            op |= PGSTAT_FETCH_NOWAIT;
+
+        cxt->mydbentry = pgstat_get_db_entry(MyDatabaseId, op, NULL);
+
+        /* Lock failure, return. */
+        if (cxt->mydbentry == NULL)
+            return false;
+
+        cxt->mygeneration = pin_hashes(cxt->mydbentry);
+    }
+
+    LWLockAcquire(&cxt->mydbentry->lock, LW_EXCLUSIVE);
+    if (have_recovery_conflicts)
+        pgstat_flush_recovery_conflict(cxt->mydbentry);
+    if (n_deadlocks != 0)
+        pgstat_flush_deadlock(cxt->mydbentry);
+    if (n_tmpfiles != 0)
+        pgstat_flush_tempfile(cxt->mydbentry);
+    LWLockRelease(&cxt->mydbentry->lock);
+
+    return true;
+}
 
 /* ----------
  * pgstat_vacuum_stat() -
  *
- *    Will tell the collector about objects he can get rid of.
+ *    Remove objects he can get rid of.
  * ----------
  */
 void
 pgstat_vacuum_stat(void)
 {
-    HTAB       *htab;
-    PgStat_MsgTabpurge msg;
-    PgStat_MsgFuncpurge f_msg;
-    HASH_SEQ_STATUS hstat;
+    HTAB       *oidtab;
+    dshash_table *dshtable;
+    dshash_seq_status dshstat;
     PgStat_StatDBEntry *dbentry;
     PgStat_StatTabEntry *tabentry;
     PgStat_StatFuncEntry *funcentry;
-    int            len;
 
-    if (pgStatSock == PGINVALID_SOCKET)
+    /* we don't collect statistics under standalone mode */
+    if (!IsUnderPostmaster)
         return;
 
-    /*
-     * If not done for this transaction, read the statistics collector stats
-     * file into some hash tables.
-     */
-    backend_read_statsfile();
+    /* If not done for this transaction, take a snapshot of stats */
+    pgstat_snapshot_global_stats();
 
     /*
      * Read pg_database and make a list of OIDs of all existing databases
      */
-    htab = pgstat_collect_oids(DatabaseRelationId, Anum_pg_database_oid);
+    oidtab = pgstat_collect_oids(DatabaseRelationId, Anum_pg_database_oid);
 
     /*
-     * Search the database hash table for dead databases and tell the
-     * collector to drop them.
+     * Search the database hash table for dead databases and drop them
+     * from the hash.
      */
-    hash_seq_init(&hstat, pgStatDBHash);
-    while ((dbentry = (PgStat_StatDBEntry *) hash_seq_search(&hstat)) != NULL)
+
+    dshash_seq_init(&dshstat, pgStatDBHash, false, true);
+    while ((dbentry = (PgStat_StatDBEntry *) dshash_seq_next(&dshstat)) != NULL)
     {
         Oid            dbid = dbentry->databaseid;
 
@@ -1056,137 +1115,77 @@ pgstat_vacuum_stat(void)
 
         /* the DB entry for shared tables (with InvalidOid) is never dropped */
         if (OidIsValid(dbid) &&
-            hash_search(htab, (void *) &dbid, HASH_FIND, NULL) == NULL)
+            hash_search(oidtab, (void *) &dbid, HASH_FIND, NULL) == NULL)
             pgstat_drop_database(dbid);
     }
 
     /* Clean up */
-    hash_destroy(htab);
+    hash_destroy(oidtab);
 
     /*
      * Lookup our own database entry; if not found, nothing more to do.
      */
-    dbentry = (PgStat_StatDBEntry *) hash_search(pgStatDBHash,
-                                                 (void *) &MyDatabaseId,
-                                                 HASH_FIND, NULL);
-    if (dbentry == NULL || dbentry->tables == NULL)
+    dbentry = pgstat_get_db_entry(MyDatabaseId, PGSTAT_FETCH_EXCLUSIVE, NULL);
+    if (!dbentry)
         return;
 
     /*
      * Similarly to above, make a list of all known relations in this DB.
      */
-    htab = pgstat_collect_oids(RelationRelationId, Anum_pg_class_oid);
-
-    /*
-     * Initialize our messages table counter to zero
-     */
-    msg.m_nentries = 0;
+    oidtab = pgstat_collect_oids(RelationRelationId, Anum_pg_class_oid);
 
     /*
      * Check for all tables listed in stats hashtable if they still exist.
+     * Stats cache is useless here so directly search the shared hash.
      */
-    hash_seq_init(&hstat, dbentry->tables);
-    while ((tabentry = (PgStat_StatTabEntry *) hash_seq_search(&hstat)) != NULL)
+    dshtable = dshash_attach(area, &dsh_tblparams, dbentry->tables, 0);
+    dshash_seq_init(&dshstat, dshtable, false, true);
+    while ((tabentry = (PgStat_StatTabEntry *) dshash_seq_next(&dshstat)) != NULL)
     {
         Oid            tabid = tabentry->tableid;
 
         CHECK_FOR_INTERRUPTS();
 
-        if (hash_search(htab, (void *) &tabid, HASH_FIND, NULL) != NULL)
+        if (hash_search(oidtab, (void *) &tabid, HASH_FIND, NULL) != NULL)
             continue;
 
-        /*
-         * Not there, so add this table's Oid to the message
-         */
-        msg.m_tableid[msg.m_nentries++] = tabid;
-
-        /*
-         * If the message is full, send it out and reinitialize to empty
-         */
-        if (msg.m_nentries >= PGSTAT_NUM_TABPURGE)
-        {
-            len = offsetof(PgStat_MsgTabpurge, m_tableid[0])
-                + msg.m_nentries * sizeof(Oid);
-
-            pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_TABPURGE);
-            msg.m_databaseid = MyDatabaseId;
-            pgstat_send(&msg, len);
-
-            msg.m_nentries = 0;
-        }
-    }
-
-    /*
-     * Send the rest
-     */
-    if (msg.m_nentries > 0)
-    {
-        len = offsetof(PgStat_MsgTabpurge, m_tableid[0])
-            + msg.m_nentries * sizeof(Oid);
-
-        pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_TABPURGE);
-        msg.m_databaseid = MyDatabaseId;
-        pgstat_send(&msg, len);
+        /* Not there, so purge this table */
+        dshash_delete_entry(dshtable, tabentry);
     }
+    dshash_detach(dshtable);
 
     /* Clean up */
-    hash_destroy(htab);
+    hash_destroy(oidtab);
 
     /*
      * Now repeat the above steps for functions.  However, we needn't bother
      * in the common case where no function stats are being collected.
      */
-    if (dbentry->functions != NULL &&
-        hash_get_num_entries(dbentry->functions) > 0)
+    if (dbentry->functions != DSM_HANDLE_INVALID)
     {
-        htab = pgstat_collect_oids(ProcedureRelationId, Anum_pg_proc_oid);
+        dshtable =
+            dshash_attach(area, &dsh_funcparams, dbentry->functions, 0);
+        oidtab = pgstat_collect_oids(ProcedureRelationId, Anum_pg_proc_oid);
 
-        pgstat_setheader(&f_msg.m_hdr, PGSTAT_MTYPE_FUNCPURGE);
-        f_msg.m_databaseid = MyDatabaseId;
-        f_msg.m_nentries = 0;
-
-        hash_seq_init(&hstat, dbentry->functions);
-        while ((funcentry = (PgStat_StatFuncEntry *) hash_seq_search(&hstat)) != NULL)
+        dshash_seq_init(&dshstat, dshtable, false, true);
+        while ((funcentry = (PgStat_StatFuncEntry *) dshash_seq_next(&dshstat)) != NULL)
         {
             Oid            funcid = funcentry->functionid;
 
             CHECK_FOR_INTERRUPTS();
 
-            if (hash_search(htab, (void *) &funcid, HASH_FIND, NULL) != NULL)
+            if (hash_search(oidtab, (void *) &funcid, HASH_FIND, NULL) != NULL)
                 continue;
 
-            /*
-             * Not there, so add this function's Oid to the message
-             */
-            f_msg.m_functionid[f_msg.m_nentries++] = funcid;
-
-            /*
-             * If the message is full, send it out and reinitialize to empty
-             */
-            if (f_msg.m_nentries >= PGSTAT_NUM_FUNCPURGE)
-            {
-                len = offsetof(PgStat_MsgFuncpurge, m_functionid[0])
-                    + f_msg.m_nentries * sizeof(Oid);
-
-                pgstat_send(&f_msg, len);
-
-                f_msg.m_nentries = 0;
-            }
+            /* Not there, so remove this function */
+            dshash_delete_entry(dshtable, funcentry);
         }
 
-        /*
-         * Send the rest
-         */
-        if (f_msg.m_nentries > 0)
-        {
-            len = offsetof(PgStat_MsgFuncpurge, m_functionid[0])
-                + f_msg.m_nentries * sizeof(Oid);
+        hash_destroy(oidtab);
 
-            pgstat_send(&f_msg, len);
-        }
-
-        hash_destroy(htab);
+        dshash_detach(dshtable);
     }
+    dshash_release_lock(pgStatDBHash, dbentry);
 }
 
 
@@ -1244,62 +1243,57 @@ pgstat_collect_oids(Oid catalogid, AttrNumber anum_oid)
 /* ----------
  * pgstat_drop_database() -
  *
- *    Tell the collector that we just dropped a database.
- *    (If the message gets lost, we will still clean the dead DB eventually
- *    via future invocations of pgstat_vacuum_stat().)
+ *    Remove entry for the database that we just dropped.
+ *
+ *    If some stats are flushed after this, this entry will re-created but we
+ *    will still clean the dead DB eventually via future invocations of
+ *    pgstat_vacuum_stat().
  * ----------
  */
 void
 pgstat_drop_database(Oid databaseid)
 {
-    PgStat_MsgDropdb msg;
+    PgStat_StatDBEntry *dbentry;
 
-    if (pgStatSock == PGINVALID_SOCKET)
-        return;
+    Assert (OidIsValid(databaseid));
+    Assert(pgStatDBHash);
 
-    pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_DROPDB);
-    msg.m_databaseid = databaseid;
-    pgstat_send(&msg, sizeof(msg));
+    /*
+     * Lookup the database in the hashtable with exclusive lock.
+     */
+    dbentry = pgstat_get_db_entry(databaseid, PGSTAT_FETCH_EXCLUSIVE, NULL);
+
+    /*
+     * If found, remove it (along with the db statfile).
+     */
+    if (dbentry)
+    {
+        LWLockAcquire(&dbentry->lock, LW_EXCLUSIVE);
+        Assert(dbentry->refcnt == 0);
+
+        /* One one must live on this database. It's safe to drop all. */
+        if (dbentry->tables != DSM_HANDLE_INVALID)
+        {
+            dshash_table *tbl =
+                dshash_attach(area, &dsh_tblparams, dbentry->tables, 0);
+            dshash_destroy(tbl);
+        }
+        if (dbentry->functions != DSM_HANDLE_INVALID)
+        {
+            dshash_table *tbl =
+                dshash_attach(area, &dsh_funcparams, dbentry->functions, 0);
+            dshash_destroy(tbl);
+        }
+        LWLockRelease(&dbentry->lock);
+
+        dshash_delete_entry(pgStatDBHash, (void *)dbentry);
+    }
 }
 
-
-/* ----------
- * pgstat_drop_relation() -
- *
- *    Tell the collector that we just dropped a relation.
- *    (If the message gets lost, we will still clean the dead entry eventually
- *    via future invocations of pgstat_vacuum_stat().)
- *
- *    Currently not used for lack of any good place to call it; we rely
- *    entirely on pgstat_vacuum_stat() to clean out stats for dead rels.
- * ----------
- */
-#ifdef NOT_USED
-void
-pgstat_drop_relation(Oid relid)
-{
-    PgStat_MsgTabpurge msg;
-    int            len;
-
-    if (pgStatSock == PGINVALID_SOCKET)
-        return;
-
-    msg.m_tableid[0] = relid;
-    msg.m_nentries = 1;
-
-    len = offsetof(PgStat_MsgTabpurge, m_tableid[0]) + sizeof(Oid);
-
-    pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_TABPURGE);
-    msg.m_databaseid = MyDatabaseId;
-    pgstat_send(&msg, len);
-}
-#endif                            /* NOT_USED */
-
-
 /* ----------
  * pgstat_reset_counters() -
  *
- *    Tell the statistics collector to reset counters for our database.
+ *    Reset counters for our database.
  *
  *    Permission checking for this function is managed through the normal
  *    GRANT system.
@@ -1308,20 +1302,31 @@ pgstat_drop_relation(Oid relid)
 void
 pgstat_reset_counters(void)
 {
-    PgStat_MsgResetcounter msg;
+    PgStat_StatDBEntry       *dbentry;
+    PgStat_TableLookupState status;
 
-    if (pgStatSock == PGINVALID_SOCKET)
+    Assert(pgStatDBHash);
+
+    /*
+     * Lookup the database in the hashtable.  Nothing to do if not there.
+     */
+    dbentry = pgstat_get_db_entry(MyDatabaseId, PGSTAT_FETCH_EXCLUSIVE, &status);
+
+    if (!dbentry)
         return;
 
-    pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RESETCOUNTER);
-    msg.m_databaseid = MyDatabaseId;
-    pgstat_send(&msg, sizeof(msg));
+    /* This database is active, safe to release the lock immediately. */
+    dshash_release_lock(pgStatDBHash, dbentry);
+
+    /* Reset database-level stats. */
+    reset_dbentry_counters(dbentry);
+
 }
 
 /* ----------
  * pgstat_reset_shared_counters() -
  *
- *    Tell the statistics collector to reset cluster-wide shared counters.
+ *    Reset cluster-wide shared counters.
  *
  *    Permission checking for this function is managed through the normal
  *    GRANT system.
@@ -1330,29 +1335,35 @@ pgstat_reset_counters(void)
 void
 pgstat_reset_shared_counters(const char *target)
 {
-    PgStat_MsgResetsharedcounter msg;
-
-    if (pgStatSock == PGINVALID_SOCKET)
-        return;
-
+    /* Reset the archiver statistics for the cluster. */
     if (strcmp(target, "archiver") == 0)
-        msg.m_resettarget = RESET_ARCHIVER;
+    {
+        LWLockAcquire(StatsLock, LW_EXCLUSIVE);
+
+        MemSet(shared_archiverStats, 0, sizeof(*shared_archiverStats));
+        shared_archiverStats->stat_reset_timestamp = GetCurrentTimestamp();
+    }
     else if (strcmp(target, "bgwriter") == 0)
-        msg.m_resettarget = RESET_BGWRITER;
+    {
+        LWLockAcquire(StatsLock, LW_EXCLUSIVE);
+
+        /* Reset the global background writer statistics for the cluster. */
+        MemSet(shared_globalStats, 0, sizeof(*shared_globalStats));
+        shared_globalStats->stat_reset_timestamp = GetCurrentTimestamp();
+    }
     else
         ereport(ERROR,
                 (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                  errmsg("unrecognized reset target: \"%s\"", target),
                  errhint("Target must be \"archiver\" or \"bgwriter\".")));
 
-    pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RESETSHAREDCOUNTER);
-    pgstat_send(&msg, sizeof(msg));
+    LWLockRelease(StatsLock);
 }
 
 /* ----------
  * pgstat_reset_single_counter() -
  *
- *    Tell the statistics collector to reset a single counter.
+ *    Reset a single counter.
  *
  *    Permission checking for this function is managed through the normal
  *    GRANT system.
@@ -1361,17 +1372,42 @@ pgstat_reset_shared_counters(const char *target)
 void
 pgstat_reset_single_counter(Oid objoid, PgStat_Single_Reset_Type type)
 {
-    PgStat_MsgResetsinglecounter msg;
+    PgStat_StatDBEntry *dbentry;
+    TimestampTz ts;
+    int generation;
 
-    if (pgStatSock == PGINVALID_SOCKET)
+    dbentry = pgstat_get_db_entry(MyDatabaseId, PGSTAT_FETCH_EXCLUSIVE, NULL);
+
+    if (!dbentry)
         return;
 
-    pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RESETSINGLECOUNTER);
-    msg.m_databaseid = MyDatabaseId;
-    msg.m_resettype = type;
-    msg.m_objectid = objoid;
+    /* This database is active, safe to release the lock immediately. */
+    generation = pin_hashes(dbentry);
 
-    pgstat_send(&msg, sizeof(msg));
+    /* Set the reset timestamp for the whole database */
+    ts = GetCurrentTimestamp();
+    LWLockAcquire(&dbentry->lock, LW_EXCLUSIVE);
+    dbentry->stat_reset_timestamp = ts;
+    LWLockRelease(&dbentry->lock);
+
+    /* Remove object if it exists, ignore if not */
+    if (type == RESET_TABLE)
+    {
+        dshash_table *t = attach_table_hash(dbentry, generation);
+        dshash_delete_key(t, (void *) &objoid);
+        dshash_detach(t);
+    }
+
+    if (type == RESET_FUNCTION)
+    {
+        dshash_table *t = attach_function_hash(dbentry, generation);
+        if (t)
+        {
+            dshash_delete_key(t, (void *) &objoid);
+            dshash_detach(t);
+        }
+    }
+    unpin_hashes(dbentry, generation);
 }
 
 /* ----------
@@ -1385,48 +1421,83 @@ pgstat_reset_single_counter(Oid objoid, PgStat_Single_Reset_Type type)
 void
 pgstat_report_autovac(Oid dboid)
 {
-    PgStat_MsgAutovacStart msg;
+    PgStat_StatDBEntry *dbentry;
+    TimestampTz ts;
 
-    if (pgStatSock == PGINVALID_SOCKET)
+    Assert(pgStatDBHash);
+
+    if (!pgstat_track_counts || !IsUnderPostmaster)
         return;
 
-    pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_AUTOVAC_START);
-    msg.m_databaseid = dboid;
-    msg.m_start_time = GetCurrentTimestamp();
+    /*
+     * Store the last autovacuum time in the database's hashtable entry.
+     */
+    dbentry = pgstat_get_db_entry(dboid, PGSTAT_FETCH_EXCLUSIVE, NULL);
+    dshash_release_lock(pgStatDBHash, dbentry);
 
-    pgstat_send(&msg, sizeof(msg));
+    ts = GetCurrentTimestamp();
+
+    LWLockAcquire(&dbentry->lock, LW_EXCLUSIVE);
+    dbentry->last_autovac_time = ts;
+    LWLockRelease(&dbentry->lock);
 }
 
 
 /* ---------
  * pgstat_report_vacuum() -
  *
- *    Tell the collector about the table we just vacuumed.
+ *    Report about the table we just vacuumed.
  * ---------
  */
 void
 pgstat_report_vacuum(Oid tableoid, bool shared,
                      PgStat_Counter livetuples, PgStat_Counter deadtuples)
 {
-    PgStat_MsgVacuum msg;
+    Oid                    dboid;
+    PgStat_StatDBEntry *dbentry;
+    PgStat_StatTabEntry *tabentry;
+    dshash_table *table;
+    int                    generation;
 
-    if (pgStatSock == PGINVALID_SOCKET || !pgstat_track_counts)
+    Assert(pgStatDBHash);
+
+    if (!pgstat_track_counts || !IsUnderPostmaster)
         return;
 
-    pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_VACUUM);
-    msg.m_databaseid = shared ? InvalidOid : MyDatabaseId;
-    msg.m_tableoid = tableoid;
-    msg.m_autovacuum = IsAutoVacuumWorkerProcess();
-    msg.m_vacuumtime = GetCurrentTimestamp();
-    msg.m_live_tuples = livetuples;
-    msg.m_dead_tuples = deadtuples;
-    pgstat_send(&msg, sizeof(msg));
+    dboid = shared ? InvalidOid : MyDatabaseId;
+
+    /*
+     * Store the data in the table's hash table entry.
+     */
+    dbentry = pgstat_get_db_entry(dboid, PGSTAT_FETCH_EXCLUSIVE, NULL);
+    generation = pin_hashes(dbentry);
+    table = attach_table_hash(dbentry, generation);
+
+    tabentry = pgstat_get_tab_entry(table, tableoid, true);
+
+    tabentry->n_live_tuples = livetuples;
+    tabentry->n_dead_tuples = deadtuples;
+
+    if (IsAutoVacuumWorkerProcess())
+    {
+        tabentry->autovac_vacuum_timestamp = GetCurrentTimestamp();
+        tabentry->autovac_vacuum_count++;
+    }
+    else
+    {
+        tabentry->vacuum_timestamp = GetCurrentTimestamp();
+        tabentry->vacuum_count++;
+    }
+    dshash_release_lock(table, tabentry);
+
+    dshash_detach(table);
+    unpin_hashes(dbentry, generation);
 }
 
 /* --------
  * pgstat_report_analyze() -
  *
- *    Tell the collector about the table we just analyzed.
+ *    Report about the table we just analyzed.
  *
  * Caller must provide new live- and dead-tuples estimates, as well as a
  * flag indicating whether to reset the changes_since_analyze counter.
@@ -1437,9 +1508,15 @@ pgstat_report_analyze(Relation rel,
                       PgStat_Counter livetuples, PgStat_Counter deadtuples,
                       bool resetcounter)
 {
-    PgStat_MsgAnalyze msg;
+    Oid                    dboid;
+    PgStat_StatDBEntry *dbentry;
+    PgStat_StatTabEntry *tabentry;
+    dshash_table       *table;
+    int                    generation;
 
-    if (pgStatSock == PGINVALID_SOCKET || !pgstat_track_counts)
+    Assert(pgStatDBHash);
+
+    if (!pgstat_track_counts || !IsUnderPostmaster)
         return;
 
     /*
@@ -1468,114 +1545,217 @@ pgstat_report_analyze(Relation rel,
         deadtuples = Max(deadtuples, 0);
     }
 
-    pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_ANALYZE);
-    msg.m_databaseid = rel->rd_rel->relisshared ? InvalidOid : MyDatabaseId;
-    msg.m_tableoid = RelationGetRelid(rel);
-    msg.m_autovacuum = IsAutoVacuumWorkerProcess();
-    msg.m_resetcounter = resetcounter;
-    msg.m_analyzetime = GetCurrentTimestamp();
-    msg.m_live_tuples = livetuples;
-    msg.m_dead_tuples = deadtuples;
-    pgstat_send(&msg, sizeof(msg));
+    dboid = rel->rd_rel->relisshared ? InvalidOid : MyDatabaseId;
+
+    /*
+     * Store the data in the table's hashtable entry.
+     */
+    dbentry = pgstat_get_db_entry(dboid, PGSTAT_FETCH_EXCLUSIVE, NULL);
+    generation = pin_hashes(dbentry);
+    table = attach_table_hash(dbentry, generation);
+    tabentry = pgstat_get_tab_entry(table, RelationGetRelid(rel), true);
+
+    tabentry->n_live_tuples = livetuples;
+    tabentry->n_dead_tuples = deadtuples;
+
+    /*
+     * If commanded, reset changes_since_analyze to zero.  This forgets any
+     * changes that were committed while the ANALYZE was in progress, but we
+     * have no good way to estimate how many of those there were.
+     */
+    if (resetcounter)
+        tabentry->changes_since_analyze = 0;
+
+    if (IsAutoVacuumWorkerProcess())
+    {
+        tabentry->autovac_analyze_timestamp = GetCurrentTimestamp();
+        tabentry->autovac_analyze_count++;
+    }
+    else
+    {
+        tabentry->analyze_timestamp = GetCurrentTimestamp();
+        tabentry->analyze_count++;
+    }
+    dshash_release_lock(table, tabentry);
+
+    dshash_detach(table);
+    unpin_hashes(dbentry, generation);
 }
 
 /* --------
  * pgstat_report_recovery_conflict() -
  *
- *    Tell the collector about a Hot Standby recovery conflict.
+ *    Report a Hot Standby recovery conflict.
  * --------
  */
 void
 pgstat_report_recovery_conflict(int reason)
 {
-    PgStat_MsgRecoveryConflict msg;
+    PgStat_StatDBEntry *dbentry;
+    PgStat_TableLookupState status;
 
-    if (pgStatSock == PGINVALID_SOCKET || !pgstat_track_counts)
+    Assert(pgStatDBHash);
+
+    if (!pgstat_track_counts || !IsUnderPostmaster)
         return;
 
-    pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RECOVERYCONFLICT);
-    msg.m_databaseid = MyDatabaseId;
-    msg.m_reason = reason;
-    pgstat_send(&msg, sizeof(msg));
+    have_recovery_conflicts = true;
+
+    switch (reason)
+    {
+        case PROCSIG_RECOVERY_CONFLICT_DATABASE:
+
+            /*
+             * Since we drop the information about the database as soon as it
+             * replicates, there is no point in counting these conflicts.
+             */
+            break;
+        case PROCSIG_RECOVERY_CONFLICT_TABLESPACE:
+            n_conflict_tablespace++;
+            break;
+        case PROCSIG_RECOVERY_CONFLICT_LOCK:
+            n_conflict_lock++;
+            break;
+        case PROCSIG_RECOVERY_CONFLICT_SNAPSHOT:
+            n_conflict_snapshot++;
+            break;
+        case PROCSIG_RECOVERY_CONFLICT_BUFFERPIN:
+            n_conflict_bufferpin++;
+            break;
+        case PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK:
+            n_conflict_startup_deadlock++;
+            break;
+    }
+
+    dbentry = pgstat_get_db_entry(MyDatabaseId,
+                                  PGSTAT_FETCH_EXCLUSIVE | PGSTAT_FETCH_NOWAIT,
+                                  &status);
+
+    if (status == PGSTAT_ENTRY_LOCK_FAILED)
+        return;
+
+    /* We had a chance to flush immediately */
+    pgstat_flush_recovery_conflict(dbentry);
+
+    dshash_release_lock(pgStatDBHash, dbentry);
+}
+
+/*
+ * flush recovery conflict stats
+ */
+static void
+pgstat_flush_recovery_conflict(PgStat_StatDBEntry *dbentry)
+{
+    dbentry->n_conflict_tablespace    += n_conflict_tablespace;
+    dbentry->n_conflict_lock         += n_conflict_lock;
+    dbentry->n_conflict_snapshot    += n_conflict_snapshot;
+    dbentry->n_conflict_bufferpin    += n_conflict_bufferpin;
+    dbentry->n_conflict_startup_deadlock += n_conflict_startup_deadlock;
+
+    n_conflict_tablespace = 0;
+    n_conflict_lock = 0;
+    n_conflict_snapshot = 0;
+    n_conflict_bufferpin = 0;
+    n_conflict_startup_deadlock = 0;
+
+    have_recovery_conflicts = false;
 }
 
 /* --------
  * pgstat_report_deadlock() -
  *
- *    Tell the collector about a deadlock detected.
+ *    Report a deadlock detected.
  * --------
  */
 void
 pgstat_report_deadlock(void)
 {
-    PgStat_MsgDeadlock msg;
+    PgStat_StatDBEntry *dbentry;
+    PgStat_TableLookupState status;
 
-    if (pgStatSock == PGINVALID_SOCKET || !pgstat_track_counts)
+    Assert(pgStatDBHash);
+
+    if (!pgstat_track_counts || !IsUnderPostmaster)
         return;
 
-    pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_DEADLOCK);
-    msg.m_databaseid = MyDatabaseId;
-    pgstat_send(&msg, sizeof(msg));
+    n_deadlocks++;
+
+    dbentry = pgstat_get_db_entry(MyDatabaseId,
+                                  PGSTAT_FETCH_EXCLUSIVE | PGSTAT_FETCH_NOWAIT,
+                                  &status);
+
+    if (status == PGSTAT_ENTRY_LOCK_FAILED)
+        return;
+
+    /* We had a chance to flush immediately */
+    pgstat_flush_deadlock(dbentry);
+
+    dshash_release_lock(pgStatDBHash, dbentry);
+}
+
+/*
+ * flush dead lock stats
+ */
+static void
+pgstat_flush_deadlock(PgStat_StatDBEntry *dbentry)
+{
+    dbentry->n_deadlocks += n_deadlocks;
+    n_deadlocks = 0;
 }
 
 /* --------
  * pgstat_report_tempfile() -
  *
- *    Tell the collector about a temporary file.
+ *    Report a temporary file.
  * --------
  */
 void
 pgstat_report_tempfile(size_t filesize)
 {
-    PgStat_MsgTempFile msg;
+    PgStat_StatDBEntry *dbentry;
+    PgStat_TableLookupState status;
 
-    if (pgStatSock == PGINVALID_SOCKET || !pgstat_track_counts)
+    Assert(pgStatDBHash);
+
+    if (!pgstat_track_counts || !IsUnderPostmaster)
         return;
 
-    pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_TEMPFILE);
-    msg.m_databaseid = MyDatabaseId;
-    msg.m_filesize = filesize;
-    pgstat_send(&msg, sizeof(msg));
-}
+    if (filesize > 0) /* Is there a case where filesize is really 0? */
+    {
+        n_tmpfilesize += filesize; /* needs check overflow */
+        n_tmpfiles++;
+    }
 
-
-/* ----------
- * pgstat_ping() -
- *
- *    Send some junk data to the collector to increase traffic.
- * ----------
- */
-void
-pgstat_ping(void)
-{
-    PgStat_MsgDummy msg;
-
-    if (pgStatSock == PGINVALID_SOCKET)
+    if (n_tmpfiles == 0)
         return;
 
-    pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_DUMMY);
-    pgstat_send(&msg, sizeof(msg));
+    dbentry = pgstat_get_db_entry(MyDatabaseId,
+                                  PGSTAT_FETCH_EXCLUSIVE | PGSTAT_FETCH_NOWAIT,
+                                  &status);
+
+    if (status == PGSTAT_ENTRY_LOCK_FAILED)
+        return;
+
+    /* We had a chance to flush immediately */
+    pgstat_flush_tempfile(dbentry);
+
+    dshash_release_lock(pgStatDBHash, dbentry);
 }
 
-/* ----------
- * pgstat_send_inquiry() -
- *
- *    Notify collector that we need fresh data.
- * ----------
+/*
+ * flush temporary file stats
  */
 static void
-pgstat_send_inquiry(TimestampTz clock_time, TimestampTz cutoff_time, Oid databaseid)
+pgstat_flush_tempfile(PgStat_StatDBEntry *dbentry)
 {
-    PgStat_MsgInquiry msg;
 
-    pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_INQUIRY);
-    msg.clock_time = clock_time;
-    msg.cutoff_time = cutoff_time;
-    msg.databaseid = databaseid;
-    pgstat_send(&msg, sizeof(msg));
+    dbentry->n_temp_bytes += n_tmpfilesize;
+    dbentry->n_temp_files += n_tmpfiles;
+    n_tmpfilesize = 0;
+    n_tmpfiles = 0;
+
 }
 
-
 /*
  * Initialize function call usage data.
  * Called by the executor before invoking a function.
@@ -1726,7 +1906,7 @@ pgstat_initstats(Relation rel)
         return;
     }
 
-    if (pgStatSock == PGINVALID_SOCKET || !pgstat_track_counts)
+    if (!pgstat_track_counts || !IsUnderPostmaster)
     {
         /* We're not counting at all */
         rel->pgstat_info = NULL;
@@ -1745,6 +1925,24 @@ pgstat_initstats(Relation rel)
     rel->pgstat_info = get_tabstat_entry(rel_id, rel->rd_rel->relisshared);
 }
 
+/*
+ * create_tabstat_hash - create local hash as transactional storage
+ */
+static HTAB *
+create_tabstat_hash(void)
+{
+    HASHCTL        ctl;
+
+    MemSet(&ctl, 0, sizeof(ctl));
+    ctl.keysize = sizeof(Oid);
+    ctl.entrysize = sizeof(TabStatHashEntry);
+
+    return hash_create("pgstat TabStatusArray lookup hash table",
+                       TABSTAT_QUANTUM,
+                       &ctl,
+                       HASH_ELEM | HASH_BLOBS);
+}
+
 /*
  * get_tabstat_entry - find or create a PgStat_TableStatus entry for rel
  */
@@ -1760,18 +1958,7 @@ get_tabstat_entry(Oid rel_id, bool isshared)
      * Create hash table if we don't have it already.
      */
     if (pgStatTabHash == NULL)
-    {
-        HASHCTL        ctl;
-
-        memset(&ctl, 0, sizeof(ctl));
-        ctl.keysize = sizeof(Oid);
-        ctl.entrysize = sizeof(TabStatHashEntry);
-
-        pgStatTabHash = hash_create("pgstat TabStatusArray lookup hash table",
-                                    TABSTAT_QUANTUM,
-                                    &ctl,
-                                    HASH_ELEM | HASH_BLOBS);
-    }
+        pgStatTabHash = create_tabstat_hash();
 
     /*
      * Find an entry or create a new one.
@@ -2125,8 +2312,8 @@ AtEOXact_PgStat(bool isCommit)
     }
     pgStatXactStack = NULL;
 
-    /* Make sure any stats snapshot is thrown away */
-    pgstat_clear_snapshot();
+    /* mark as the next reference is the first in a transaction */
+    first_in_xact = true;
 }
 
 /* ----------
@@ -2307,8 +2494,8 @@ PostPrepare_PgStat(void)
     }
     pgStatXactStack = NULL;
 
-    /* Make sure any stats snapshot is thrown away */
-    pgstat_clear_snapshot();
+    /* mark as the next reference is the first in a transaction */
+    first_in_xact = true;
 }
 
 /*
@@ -2380,30 +2567,37 @@ pgstat_twophase_postabort(TransactionId xid, uint16 info,
 /* ----------
  * pgstat_fetch_stat_dbentry() -
  *
- *    Support function for the SQL-callable pgstat* functions. Returns
- *    the collected statistics for one database or NULL. NULL doesn't mean
- *    that the database doesn't exist, it is just not yet known by the
- *    collector, so the caller is better off to report ZERO instead.
- * ----------
+ *    Find database stats entry on backends. The returned entries are cached
+ *    until transaction end or pgstat_clear_snapshot() is called.
  */
 PgStat_StatDBEntry *
 pgstat_fetch_stat_dbentry(Oid dbid)
 {
-    /*
-     * If not done for this transaction, read the statistics collector stats
-     * file into some hash tables.
-     */
-    backend_read_statsfile();
+    /* context for snapshot_statentry */
+    static pgstat_snapshot_cxt cxt =
+    {
+        .hash_name = "local database stats hash",
+        .hash = NULL,
+        .hash_entsize = sizeof(PgStat_StatDBEntry_snapshot),
+        .dshash = NULL,
+        .dsh_handle = DSM_HANDLE_INVALID,
+        .dsh_params = &dsh_dbparams
+    };
 
-    /*
-     * Lookup the requested database; return NULL if not found
-     */
-    return (PgStat_StatDBEntry *) hash_search(pgStatDBHash,
-                                              (void *) &dbid,
-                                              HASH_FIND, NULL);
+    /* should be called from backends  */
+    Assert(IsUnderPostmaster);
+
+    /* If not done for this transaction, take a snapshot of global stats */
+    pgstat_snapshot_global_stats();
+
+    cxt.dshash = &pgStatDBHash;
+    cxt.hash = &pgStatDBEntrySnapshot;
+
+    /* caller doesn't have a business with snapshot-local members  */
+    return (PgStat_StatDBEntry *)
+        snapshot_statentry(&cxt, dbid);
 }
 
-
 /* ----------
  * pgstat_fetch_stat_tabentry() -
  *
@@ -2416,51 +2610,66 @@ pgstat_fetch_stat_dbentry(Oid dbid)
 PgStat_StatTabEntry *
 pgstat_fetch_stat_tabentry(Oid relid)
 {
-    Oid            dbid;
     PgStat_StatDBEntry *dbentry;
     PgStat_StatTabEntry *tabentry;
 
-    /*
-     * If not done for this transaction, read the statistics collector stats
-     * file into some hash tables.
-     */
-    backend_read_statsfile();
+    /* Lookup our database, then look in its table hash table. */
+    dbentry = pgstat_fetch_stat_dbentry(MyDatabaseId);
+    if (dbentry == NULL)
+        return NULL;
 
-    /*
-     * Lookup our database, then look in its table hash table.
-     */
-    dbid = MyDatabaseId;
-    dbentry = (PgStat_StatDBEntry *) hash_search(pgStatDBHash,
-                                                 (void *) &dbid,
-                                                 HASH_FIND, NULL);
-    if (dbentry != NULL && dbentry->tables != NULL)
-    {
-        tabentry = (PgStat_StatTabEntry *) hash_search(dbentry->tables,
-                                                       (void *) &relid,
-                                                       HASH_FIND, NULL);
-        if (tabentry)
-            return tabentry;
-    }
+    tabentry = pgstat_fetch_stat_tabentry_extended(dbentry, relid);
+    if (tabentry != NULL)
+        return tabentry;
 
     /*
      * If we didn't find it, maybe it's a shared table.
      */
-    dbid = InvalidOid;
-    dbentry = (PgStat_StatDBEntry *) hash_search(pgStatDBHash,
-                                                 (void *) &dbid,
-                                                 HASH_FIND, NULL);
-    if (dbentry != NULL && dbentry->tables != NULL)
-    {
-        tabentry = (PgStat_StatTabEntry *) hash_search(dbentry->tables,
-                                                       (void *) &relid,
-                                                       HASH_FIND, NULL);
-        if (tabentry)
-            return tabentry;
-    }
+    dbentry = pgstat_fetch_stat_dbentry(InvalidOid);
+    if (dbentry == NULL)
+        return NULL;
+
+    tabentry = pgstat_fetch_stat_tabentry_extended(dbentry, relid);
+    if (tabentry != NULL)
+        return tabentry;
 
     return NULL;
 }
 
+/* ----------
+ * pgstat_fetch_stat_tabentry_extended() -
+ *
+ *    Find table stats entry on backends. The returned entries are cached until
+ *    transaction end or pgstat_clear_snapshot() is called.
+ */
+PgStat_StatTabEntry *
+pgstat_fetch_stat_tabentry_extended(PgStat_StatDBEntry *dbent, Oid reloid)
+{
+    /* context for snapshot_statentry */
+    static pgstat_snapshot_cxt cxt =
+    {
+        .hash_name = "table stats snapshot hash",
+        .hash = NULL,
+        .hash_entsize = sizeof(PgStat_StatDBEntry_snapshot),
+        .dshash = NULL,
+        .dsh_handle = DSM_HANDLE_INVALID,
+        .dsh_params = &dsh_dbparams
+    };
+    PgStat_StatDBEntry_snapshot *local_dbent;
+
+    /* should be called from backends  */
+    Assert(IsUnderPostmaster);
+
+    /* dbent given to this function is alias of PgStat_StatDBEntry_snapshot */
+    local_dbent = (PgStat_StatDBEntry_snapshot *)dbent;
+    cxt.hash = &local_dbent->snapshot_tables;
+    cxt.dshash = &local_dbent->dshash_tables;
+    cxt.dsh_handle = dbent->tables;
+
+    return (PgStat_StatTabEntry *)
+        snapshot_statentry(&cxt, reloid);
+}
+
 
 /* ----------
  * pgstat_fetch_stat_funcentry() -
@@ -2475,21 +2684,125 @@ pgstat_fetch_stat_funcentry(Oid func_id)
     PgStat_StatDBEntry *dbentry;
     PgStat_StatFuncEntry *funcentry = NULL;
 
-    /* load the stats file if needed */
-    backend_read_statsfile();
-
-    /* Lookup our database, then find the requested function.  */
+    /* Lookup our database, then find the requested function */
     dbentry = pgstat_fetch_stat_dbentry(MyDatabaseId);
-    if (dbentry != NULL && dbentry->functions != NULL)
-    {
-        funcentry = (PgStat_StatFuncEntry *) hash_search(dbentry->functions,
-                                                         (void *) &func_id,
-                                                         HASH_FIND, NULL);
-    }
+    if (dbentry == NULL)
+        return NULL;
+
+    funcentry = pgstat_fetch_stat_funcentry_extended(dbentry, func_id);
 
     return funcentry;
 }
 
+/* ----------
+ * pgstat_fetch_stat_funcentry_extended() -
+ *
+ *    Find function stats entry on backends. The returned entries are cached
+ *    until transaction end or pgstat_clear_snapshot() is called.
+ */
+static PgStat_StatFuncEntry *
+pgstat_fetch_stat_funcentry_extended(PgStat_StatDBEntry *dbent, Oid funcid)
+{
+    /* context for snapshot_statentry */
+    static pgstat_snapshot_cxt cxt =
+    {
+        .hash_name = "function stats snapshot hash",
+        .hash = NULL,
+        .hash_entsize = sizeof(PgStat_StatDBEntry_snapshot),
+        .dshash = NULL,
+        .dsh_handle = DSM_HANDLE_INVALID,
+        .dsh_params = &dsh_dbparams
+    };
+    PgStat_StatDBEntry_snapshot *local_dbent;
+
+    /* should be called from backends  */
+    Assert(IsUnderPostmaster);
+
+    if (dbent->functions == DSM_HANDLE_INVALID)
+        return NULL;
+
+    /* dbent given to this function is alias of PgStat_StatDBEntry_snapshot */
+    local_dbent = (PgStat_StatDBEntry_snapshot *)dbent;
+    cxt.hash = &local_dbent->snapshot_functions;
+    cxt.dshash = &local_dbent->dshash_functions;
+    cxt.dsh_handle = dbent->functions;
+
+    return (PgStat_StatFuncEntry *)
+        snapshot_statentry(&cxt, funcid);
+}
+
+/*
+ * pgstat_snapshot_global_stats() -
+ *
+ * Makes a snapshot of global stats if not done yet.  They will be kept until
+ * subsequent call of pgstat_clear_snapshot() or the end of the current
+ * memory context (typically TopTransactionContext).
+ */
+static void
+pgstat_snapshot_global_stats(void)
+{
+    MemoryContext oldcontext;
+    TimestampTz update_time = 0;
+
+    /* The snapshot lives within CacheMemoryContext */
+    if (pgStatSnapshotContext == NULL)
+    {
+        pgStatSnapshotContext =
+            AllocSetContextCreate(CacheMemoryContext,
+                                  "Stats snapshot context",
+                                  ALLOCSET_DEFAULT_SIZES);
+    }
+
+    /*
+     * Shared stats are updated frequently especially when many backends are
+     * running, but we don't want to reconstruct snapshot so frequently for
+     * performance reasons. Keep them at least for the same duration with
+     * minimal stats update interval of a backend. As the result snapshots may
+     * live for multiple transactions.
+     */
+    if (first_in_xact && IsTransactionState())
+    {
+        first_in_xact = false;
+        LWLockAcquire(StatsLock, LW_SHARED);
+        update_time = StatsShmem->last_update;
+        LWLockRelease(StatsLock);
+
+        if (snapshot_expires_at < update_time)
+        {
+            /* No problem to expire involving backend status */
+            pgstat_clear_snapshot();
+
+            snapshot_expires_at =
+                update_time + PGSTAT_STAT_MIN_INTERVAL * USECS_PER_SEC / 1000;
+        }
+    }
+
+    /* Nothing to do if already done */
+    if (snapshot_globalStats)
+        return;
+
+    Assert(snapshot_archiverStats == NULL);
+
+    oldcontext = MemoryContextSwitchTo(pgStatSnapshotContext);
+
+    /* global stats can be just copied  */
+    LWLockAcquire(StatsLock, LW_SHARED);
+    snapshot_globalStats = palloc(sizeof(PgStat_GlobalStats));
+    memcpy(snapshot_globalStats, shared_globalStats,
+           sizeof(PgStat_GlobalStats));
+
+    snapshot_archiverStats = palloc(sizeof(PgStat_ArchiverStats));
+    memcpy(snapshot_archiverStats, shared_archiverStats,
+           sizeof(PgStat_ArchiverStats));
+    LWLockRelease(StatsLock);
+
+    /* set the timestamp of this snapshot */
+    snapshot_globalStats->stats_timestamp = update_time;
+
+    MemoryContextSwitchTo(oldcontext);
+
+    return;
+}
 
 /* ----------
  * pgstat_fetch_stat_beentry() -
@@ -2561,9 +2874,10 @@ pgstat_fetch_stat_numbackends(void)
 PgStat_ArchiverStats *
 pgstat_fetch_stat_archiver(void)
 {
-    backend_read_statsfile();
+    /* If not done for this transaction, take a stats snapshot */
+    pgstat_snapshot_global_stats();
 
-    return &archiverStats;
+    return snapshot_archiverStats;
 }
 
 
@@ -2578,9 +2892,10 @@ pgstat_fetch_stat_archiver(void)
 PgStat_GlobalStats *
 pgstat_fetch_global(void)
 {
-    backend_read_statsfile();
+    /* If not done for this transaction, take a stats snapshot */
+    pgstat_snapshot_global_stats();
 
-    return &globalStats;
+    return snapshot_globalStats;
 }
 
 
@@ -2769,8 +3084,8 @@ pgstat_initialize(void)
         MyBEEntry = &BackendStatusArray[MaxBackends + MyAuxProcType];
     }
 
-    /* Set up a process-exit hook to clean up */
-    on_shmem_exit(pgstat_beshutdown_hook, 0);
+    /* need to be called before dsm shutodwn */
+    before_shmem_exit(pgstat_beshutdown_hook, 0);
 }
 
 /* ----------
@@ -2856,9 +3171,6 @@ pgstat_bestart(void)
             case BgWriterProcess:
                 beentry->st_backendType = B_BG_WRITER;
                 break;
-            case ArchiverProcess:
-                beentry->st_backendType = B_ARCHIVER;
-                break;
             case CheckpointerProcess:
                 beentry->st_backendType = B_CHECKPOINTER;
                 break;
@@ -3231,7 +3543,8 @@ pgstat_read_current_status(void)
 #endif
     int            i;
 
-    Assert(!pgStatRunningInCollector);
+    Assert(IsUnderPostmaster);
+
     if (localBackendStatusTable)
         return;                    /* already done */
 
@@ -3498,9 +3811,6 @@ pgstat_get_wait_activity(WaitEventActivity w)
         case WAIT_EVENT_LOGICAL_LAUNCHER_MAIN:
             event_name = "LogicalLauncherMain";
             break;
-        case WAIT_EVENT_PGSTAT_MAIN:
-            event_name = "PgStatMain";
-            break;
         case WAIT_EVENT_RECOVERY_WAL_ALL:
             event_name = "RecoveryWalAll";
             break;
@@ -4151,75 +4461,39 @@ pgstat_get_backend_desc(BackendType backendType)
  * ------------------------------------------------------------
  */
 
-
-/* ----------
- * pgstat_setheader() -
- *
- *        Set common header fields in a statistics message
- * ----------
- */
-static void
-pgstat_setheader(PgStat_MsgHdr *hdr, StatMsgType mtype)
-{
-    hdr->m_type = mtype;
-}
-
-
-/* ----------
- * pgstat_send() -
- *
- *        Send out one statistics message to the collector
- * ----------
- */
-static void
-pgstat_send(void *msg, int len)
-{
-    int            rc;
-
-    if (pgStatSock == PGINVALID_SOCKET)
-        return;
-
-    ((PgStat_MsgHdr *) msg)->m_size = len;
-
-    /* We'll retry after EINTR, but ignore all other failures */
-    do
-    {
-        rc = send(pgStatSock, msg, len, 0);
-    } while (rc < 0 && errno == EINTR);
-
-#ifdef USE_ASSERT_CHECKING
-    /* In debug builds, log send failures ... */
-    if (rc < 0)
-        elog(LOG, "could not send to statistics collector: %m");
-#endif
-}
-
 /* ----------
  * pgstat_send_archiver() -
  *
- *    Tell the collector about the WAL file that we successfully
- *    archived or failed to archive.
+ *        Report archiver statistics
  * ----------
  */
 void
 pgstat_send_archiver(const char *xlog, bool failed)
 {
-    PgStat_MsgArchiver msg;
-
-    /*
-     * Prepare and send the message
-     */
-    pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_ARCHIVER);
-    msg.m_failed = failed;
-    StrNCpy(msg.m_xlog, xlog, sizeof(msg.m_xlog));
-    msg.m_timestamp = GetCurrentTimestamp();
-    pgstat_send(&msg, sizeof(msg));
+    LWLockAcquire(StatsLock, LW_EXCLUSIVE);
+    if (failed)
+    {
+        /* Failed archival attempt */
+        ++shared_archiverStats->failed_count;
+        memcpy(shared_archiverStats->last_failed_wal, xlog,
+               sizeof(shared_archiverStats->last_failed_wal));
+        shared_archiverStats->last_failed_timestamp = GetCurrentTimestamp();
+    }
+    else
+    {
+        /* Successful archival operation */
+        ++shared_archiverStats->archived_count;
+        memcpy(shared_archiverStats->last_archived_wal, xlog,
+               sizeof(shared_archiverStats->last_archived_wal));
+        shared_archiverStats->last_archived_timestamp = GetCurrentTimestamp();
+    }
+    LWLockRelease(StatsLock);
 }
 
 /* ----------
  * pgstat_send_bgwriter() -
  *
- *        Send bgwriter statistics to the collector
+ *        Report bgwriter statistics
  * ----------
  */
 void
@@ -4228,6 +4502,8 @@ pgstat_send_bgwriter(void)
     /* We assume this initializes to zeroes */
     static const PgStat_MsgBgWriter all_zeroes;
 
+    PgStat_MsgBgWriter *s = &BgWriterStats;
+
     /*
      * This function can be called even if nothing at all has happened. In
      * this case, avoid sending a completely empty message to the stats
@@ -4236,11 +4512,18 @@ pgstat_send_bgwriter(void)
     if (memcmp(&BgWriterStats, &all_zeroes, sizeof(PgStat_MsgBgWriter)) == 0)
         return;
 
-    /*
-     * Prepare and send the message
-     */
-    pgstat_setheader(&BgWriterStats.m_hdr, PGSTAT_MTYPE_BGWRITER);
-    pgstat_send(&BgWriterStats, sizeof(BgWriterStats));
+    LWLockAcquire(StatsLock, LW_EXCLUSIVE);
+    shared_globalStats->timed_checkpoints += s->m_timed_checkpoints;
+    shared_globalStats->requested_checkpoints += s->m_requested_checkpoints;
+    shared_globalStats->checkpoint_write_time += s->m_checkpoint_write_time;
+    shared_globalStats->checkpoint_sync_time += s->m_checkpoint_sync_time;
+    shared_globalStats->buf_written_checkpoints += s->m_buf_written_checkpoints;
+    shared_globalStats->buf_written_clean += s->m_buf_written_clean;
+    shared_globalStats->maxwritten_clean += s->m_maxwritten_clean;
+    shared_globalStats->buf_written_backend += s->m_buf_written_backend;
+    shared_globalStats->buf_fsync_backend += s->m_buf_fsync_backend;
+    shared_globalStats->buf_alloc += s->m_buf_alloc;
+    LWLockRelease(StatsLock);
 
     /*
      * Clear out the statistics buffer, so it can be re-used.
@@ -4249,298 +4532,164 @@ pgstat_send_bgwriter(void)
 }
 
 
-/* ----------
- * PgstatCollectorMain() -
+/*
+ * Pin and Unpin dbentry.
  *
- *    Start up the statistics collector process.  This is the body of the
- *    postmaster child process.
- *
- *    The argc/argv parameters are valid only in EXEC_BACKEND case.
- * ----------
+ * To keep less memory usage, and for speed, counters are by recreation of
+ * dshash instead of removing entries one-by-one keeping whole-dshash lock. On
+ * the other hand dshash cannot be destroyed until all referrers have gone. As
+ * the result, other backend may be kept waiting the counter reset for not a
+ * short time. We isolate the hashes under destruction as another generation,
+ * which means no longer used but cannot be removed yet.
+
+ * When we start accessing hashes on a dbentry, call pin_hashes() and acquire
+ * the current "generation". Unlock removes the older generation's hashes when
+ * all refers have gone.
  */
-NON_EXEC_STATIC void
-PgstatCollectorMain(int argc, char *argv[])
+static int
+pin_hashes(PgStat_StatDBEntry *dbentry)
 {
-    int            len;
-    PgStat_Msg    msg;
-    int            wr;
+    int    generation;
 
-    /*
-     * Ignore all signals usually bound to some action in the postmaster,
-     * except SIGHUP and SIGQUIT.  Note we don't need a SIGUSR1 handler to
-     * support latch operations, because we only use a local latch.
-     */
-    pqsignal(SIGHUP, pgstat_sighup_handler);
-    pqsignal(SIGINT, SIG_IGN);
-    pqsignal(SIGTERM, SIG_IGN);
-    pqsignal(SIGQUIT, pgstat_exit);
-    pqsignal(SIGALRM, SIG_IGN);
-    pqsignal(SIGPIPE, SIG_IGN);
-    pqsignal(SIGUSR1, SIG_IGN);
-    pqsignal(SIGUSR2, SIG_IGN);
-    /* Reset some signals that are accepted by postmaster but not here */
-    pqsignal(SIGCHLD, SIG_DFL);
-    PG_SETMASK(&UnBlockSig);
+    LWLockAcquire(&dbentry->lock, LW_EXCLUSIVE);
+    dbentry->refcnt++;
+    generation = dbentry->generation;
+    LWLockRelease(&dbentry->lock);
 
-    /*
-     * Identify myself via ps
-     */
-    init_ps_display("stats collector", "", "", "");
+    dshash_release_lock(pgStatDBHash, dbentry);
 
-    /*
-     * Read in existing stats files or initialize the stats to zero.
-     */
-    pgStatRunningInCollector = true;
-    pgStatDBHash = pgstat_read_statsfiles(InvalidOid, true, true);
-
-    /*
-     * Loop to process messages until we get SIGQUIT or detect ungraceful
-     * death of our parent postmaster.
-     *
-     * For performance reasons, we don't want to do ResetLatch/WaitLatch after
-     * every message; instead, do that only after a recv() fails to obtain a
-     * message.  (This effectively means that if backends are sending us stuff
-     * like mad, we won't notice postmaster death until things slack off a
-     * bit; which seems fine.)    To do that, we have an inner loop that
-     * iterates as long as recv() succeeds.  We do recognize got_SIGHUP inside
-     * the inner loop, which means that such interrupts will get serviced but
-     * the latch won't get cleared until next time there is a break in the
-     * action.
-     */
-    for (;;)
-    {
-        /* Clear any already-pending wakeups */
-        ResetLatch(MyLatch);
-
-        /*
-         * Quit if we get SIGQUIT from the postmaster.
-         */
-        if (need_exit)
-            break;
-
-        /*
-         * Inner loop iterates as long as we keep getting messages, or until
-         * need_exit becomes set.
-         */
-        while (!need_exit)
-        {
-            /*
-             * Reload configuration if we got SIGHUP from the postmaster.
-             */
-            if (got_SIGHUP)
-            {
-                got_SIGHUP = false;
-                ProcessConfigFile(PGC_SIGHUP);
-            }
-
-            /*
-             * Write the stats file(s) if a new request has arrived that is
-             * not satisfied by existing file(s).
-             */
-            if (pgstat_write_statsfile_needed())
-                pgstat_write_statsfiles(false, false);
-
-            /*
-             * Try to receive and process a message.  This will not block,
-             * since the socket is set to non-blocking mode.
-             *
-             * XXX On Windows, we have to force pgwin32_recv to cooperate,
-             * despite the previous use of pg_set_noblock() on the socket.
-             * This is extremely broken and should be fixed someday.
-             */
-#ifdef WIN32
-            pgwin32_noblock = 1;
-#endif
-
-            len = recv(pgStatSock, (char *) &msg,
-                       sizeof(PgStat_Msg), 0);
-
-#ifdef WIN32
-            pgwin32_noblock = 0;
-#endif
-
-            if (len < 0)
-            {
-                if (errno == EAGAIN || errno == EWOULDBLOCK || errno == EINTR)
-                    break;        /* out of inner loop */
-                ereport(ERROR,
-                        (errcode_for_socket_access(),
-                         errmsg("could not read statistics message: %m")));
-            }
-
-            /*
-             * We ignore messages that are smaller than our common header
-             */
-            if (len < sizeof(PgStat_MsgHdr))
-                continue;
-
-            /*
-             * The received length must match the length in the header
-             */
-            if (msg.msg_hdr.m_size != len)
-                continue;
-
-            /*
-             * O.K. - we accept this message.  Process it.
-             */
-            switch (msg.msg_hdr.m_type)
-            {
-                case PGSTAT_MTYPE_DUMMY:
-                    break;
-
-                case PGSTAT_MTYPE_INQUIRY:
-                    pgstat_recv_inquiry((PgStat_MsgInquiry *) &msg, len);
-                    break;
-
-                case PGSTAT_MTYPE_TABSTAT:
-                    pgstat_recv_tabstat((PgStat_MsgTabstat *) &msg, len);
-                    break;
-
-                case PGSTAT_MTYPE_TABPURGE:
-                    pgstat_recv_tabpurge((PgStat_MsgTabpurge *) &msg, len);
-                    break;
-
-                case PGSTAT_MTYPE_DROPDB:
-                    pgstat_recv_dropdb((PgStat_MsgDropdb *) &msg, len);
-                    break;
-
-                case PGSTAT_MTYPE_RESETCOUNTER:
-                    pgstat_recv_resetcounter((PgStat_MsgResetcounter *) &msg,
-                                             len);
-                    break;
-
-                case PGSTAT_MTYPE_RESETSHAREDCOUNTER:
-                    pgstat_recv_resetsharedcounter(
-                                                   (PgStat_MsgResetsharedcounter *) &msg,
-                                                   len);
-                    break;
-
-                case PGSTAT_MTYPE_RESETSINGLECOUNTER:
-                    pgstat_recv_resetsinglecounter(
-                                                   (PgStat_MsgResetsinglecounter *) &msg,
-                                                   len);
-                    break;
-
-                case PGSTAT_MTYPE_AUTOVAC_START:
-                    pgstat_recv_autovac((PgStat_MsgAutovacStart *) &msg, len);
-                    break;
-
-                case PGSTAT_MTYPE_VACUUM:
-                    pgstat_recv_vacuum((PgStat_MsgVacuum *) &msg, len);
-                    break;
-
-                case PGSTAT_MTYPE_ANALYZE:
-                    pgstat_recv_analyze((PgStat_MsgAnalyze *) &msg, len);
-                    break;
-
-                case PGSTAT_MTYPE_ARCHIVER:
-                    pgstat_recv_archiver((PgStat_MsgArchiver *) &msg, len);
-                    break;
-
-                case PGSTAT_MTYPE_BGWRITER:
-                    pgstat_recv_bgwriter((PgStat_MsgBgWriter *) &msg, len);
-                    break;
-
-                case PGSTAT_MTYPE_FUNCSTAT:
-                    pgstat_recv_funcstat((PgStat_MsgFuncstat *) &msg, len);
-                    break;
-
-                case PGSTAT_MTYPE_FUNCPURGE:
-                    pgstat_recv_funcpurge((PgStat_MsgFuncpurge *) &msg, len);
-                    break;
-
-                case PGSTAT_MTYPE_RECOVERYCONFLICT:
-                    pgstat_recv_recoveryconflict((PgStat_MsgRecoveryConflict *) &msg, len);
-                    break;
-
-                case PGSTAT_MTYPE_DEADLOCK:
-                    pgstat_recv_deadlock((PgStat_MsgDeadlock *) &msg, len);
-                    break;
-
-                case PGSTAT_MTYPE_TEMPFILE:
-                    pgstat_recv_tempfile((PgStat_MsgTempFile *) &msg, len);
-                    break;
-
-                default:
-                    break;
-            }
-        }                        /* end of inner message-processing loop */
-
-        /* Sleep until there's something to do */
-#ifndef WIN32
-        wr = WaitLatchOrSocket(MyLatch,
-                               WL_LATCH_SET | WL_POSTMASTER_DEATH | WL_SOCKET_READABLE,
-                               pgStatSock, -1L,
-                               WAIT_EVENT_PGSTAT_MAIN);
-#else
-
-        /*
-         * Windows, at least in its Windows Server 2003 R2 incarnation,
-         * sometimes loses FD_READ events.  Waking up and retrying the recv()
-         * fixes that, so don't sleep indefinitely.  This is a crock of the
-         * first water, but until somebody wants to debug exactly what's
-         * happening there, this is the best we can do.  The two-second
-         * timeout matches our pre-9.2 behavior, and needs to be short enough
-         * to not provoke "using stale statistics" complaints from
-         * backend_read_statsfile.
-         */
-        wr = WaitLatchOrSocket(MyLatch,
-                               WL_LATCH_SET | WL_POSTMASTER_DEATH | WL_SOCKET_READABLE | WL_TIMEOUT,
-                               pgStatSock,
-                               2 * 1000L /* msec */ ,
-                               WAIT_EVENT_PGSTAT_MAIN);
-#endif
-
-        /*
-         * Emergency bailout if postmaster has died.  This is to avoid the
-         * necessity for manual cleanup of all postmaster children.
-         */
-        if (wr & WL_POSTMASTER_DEATH)
-            break;
-    }                            /* end of outer loop */
-
-    /*
-     * Save the final stats to reuse at next startup.
-     */
-    pgstat_write_statsfiles(true, true);
-
-    exit(0);
-}
-
-
-/* SIGQUIT signal handler for collector process */
-static void
-pgstat_exit(SIGNAL_ARGS)
-{
-    int            save_errno = errno;
-
-    need_exit = true;
-    SetLatch(MyLatch);
-
-    errno = save_errno;
-}
-
-/* SIGHUP handler for collector process */
-static void
-pgstat_sighup_handler(SIGNAL_ARGS)
-{
-    int            save_errno = errno;
-
-    got_SIGHUP = true;
-    SetLatch(MyLatch);
-
-    errno = save_errno;
+    return generation;
 }
 
 /*
- * Subroutine to clear stats in a database entry
+ * Unpin hashes in dbentry. If given generation is isolated, destroy it after
+ * all referrers has gone. Otherwise just decrease reference count then return.
+ */
+static void
+unpin_hashes(PgStat_StatDBEntry *dbentry, int generation)
+{
+    dshash_table *tables;
+    dshash_table *funcs = NULL;
+
+    LWLockAcquire(&dbentry->lock, LW_EXCLUSIVE);
+
+    /* using current generation, just decrease refcount */
+    if (dbentry->generation == generation)
+    {
+        dbentry->refcnt--;
+        LWLockRelease(&dbentry->lock);
+        return;
+    }
+
+    /*
+     * It is isolated, waiting for all referrers to end.
+     */
+    Assert(dbentry->generation == generation + 1);
+
+    if (--dbentry->prev_refcnt > 0)
+    {
+        LWLockRelease(&dbentry->lock);
+        return;
+    }
+
+    /* no referrer remains, remove the hashes */
+    tables = dshash_attach(area, &dsh_tblparams, dbentry->prev_tables, 0);
+    if (dbentry->prev_functions != DSM_HANDLE_INVALID)
+        funcs = dshash_attach(area, &dsh_funcparams,
+                              dbentry->prev_functions, 0);
+
+    dbentry->prev_tables = DSM_HANDLE_INVALID;
+    dbentry->prev_functions = DSM_HANDLE_INVALID;
+
+    /* release the entry immediately */
+    LWLockRelease(&dbentry->lock);
+
+    dshash_destroy(tables);
+    if (funcs)
+        dshash_destroy(funcs);
+
+    return;
+}
+
+/*
+ * attach and return the specified generation of table hash
+ * Returns NULL on lock failure.
+ */
+static dshash_table *
+attach_table_hash(PgStat_StatDBEntry *dbent, int gen)
+{
+    dshash_table *ret;
+
+    LWLockAcquire(&dbent->lock, LW_EXCLUSIVE);
+
+    if (dbent->generation == gen)
+        ret = dshash_attach(area, &dsh_tblparams, dbent->tables, 0);
+    else
+    {
+        Assert (dbent->generation == gen + 1);
+        Assert (dbent->prev_tables != DSM_HANDLE_INVALID);
+        ret = dshash_attach(area, &dsh_tblparams, dbent->prev_tables, 0);
+    }
+    LWLockRelease(&dbent->lock);
+
+    return ret;
+}
+
+/* attach and return the specified generation of function hash */
+static dshash_table *
+attach_function_hash(PgStat_StatDBEntry *dbent, int gen)
+{
+    dshash_table *ret = NULL;
+
+
+    LWLockAcquire(&dbent->lock, LW_EXCLUSIVE);
+
+    if (dbent->generation == gen)
+    {
+        if (dbent->functions == DSM_HANDLE_INVALID)
+        {
+            dshash_table *funchash =
+                dshash_create(area, &dsh_funcparams, 0);
+            dbent->functions = dshash_get_hash_table_handle(funchash);
+
+            ret = funchash;
+        }
+        else
+            ret =  dshash_attach(area, &dsh_funcparams, dbent->functions, 0);
+    }
+    /* don't bother creating useless hash */
+
+    LWLockRelease(&dbent->lock);
+
+    return  ret;
+}
+
+static void
+init_dbentry(PgStat_StatDBEntry *dbentry)
+{
+    LWLockInitialize(&dbentry->lock, LWTRANCHE_STATS);
+    dbentry->generation = 0;
+    dbentry->refcnt = 0;
+    dbentry->prev_refcnt = 0;
+    dbentry->tables = DSM_HANDLE_INVALID;
+    dbentry->prev_tables = DSM_HANDLE_INVALID;
+    dbentry->functions = DSM_HANDLE_INVALID;
+    dbentry->prev_functions = DSM_HANDLE_INVALID;
+}
+
+/*
+ * Subroutine to reset stats in a shared database entry
  *
- * Tables and functions hashes are initialized to empty.
+ * All counters are reset. Tables and functions dshashes are destroyed.  If
+ * any backend is pinning this dbentry, the current dshashes are stashed out to
+ * the previous "generation" to wait for all accessors gone. If the previous
+ * generation is already occupied, the current dshashes are so fresh that they
+ * doesn't need to be cleared.
  */
 static void
 reset_dbentry_counters(PgStat_StatDBEntry *dbentry)
 {
-    HASHCTL        hash_ctl;
+    LWLockAcquire(&dbentry->lock, LW_EXCLUSIVE);
 
     dbentry->n_xact_commit = 0;
     dbentry->n_xact_rollback = 0;
@@ -4563,23 +4712,808 @@ reset_dbentry_counters(PgStat_StatDBEntry *dbentry)
     dbentry->n_block_read_time = 0;
     dbentry->n_block_write_time = 0;
 
+    if (dbentry->refcnt == 0)
+    {
+        /*
+         * No one is referring to the current hash. Removing individual
+         * entries in dshash is very costly so just destroy it.  If someone
+         * pined this entry just after, pin_hashes returns the current
+         * generation and attach waits for the following LWLock.
+         */
+        dshash_table *tbl;
+
+        if (dbentry->tables != DSM_HANDLE_INVALID)
+        {
+            tbl = dshash_attach(area, &dsh_tblparams, dbentry->tables, 0);
+            dshash_destroy(tbl);
+            dbentry->tables = DSM_HANDLE_INVALID;
+        }
+        if (dbentry->functions != DSM_HANDLE_INVALID)
+        {
+            tbl = dshash_attach(area, &dsh_funcparams, dbentry->functions, 0);
+            dshash_destroy(tbl);
+            dbentry->functions = DSM_HANDLE_INVALID;
+        }
+    }
+    else if (dbentry->prev_refcnt == 0)
+    {
+        /*
+         * Someone is still referring to the current hash and previous slot is
+         * vacant. Stash out the current hash to the previous slot.
+         */
+        dbentry->prev_refcnt = dbentry->refcnt;
+        dbentry->prev_tables = dbentry->tables;
+        dbentry->prev_functions = dbentry->functions;
+        dbentry->refcnt = 0;
+        dbentry->tables = DSM_HANDLE_INVALID;
+        dbentry->functions = DSM_HANDLE_INVALID;
+        dbentry->generation++;
+    }
+    else
+    {
+        Assert(dbentry->prev_refcnt > 0 && dbentry->refcnt > 0);
+        /*
+         * If we get here, we just have got another reset request and the old
+         * hashes are waiting to all referrers to release. It must be quite a
+         * short time so we can just ignore this request.
+         */
+    }
+
+    /* Create new table hash if not exists */
+    if (dbentry->tables == DSM_HANDLE_INVALID)
+    {
+        dshash_table *tbl = dshash_create(area, &dsh_tblparams, 0);
+        dbentry->tables = dshash_get_hash_table_handle(tbl);
+        dshash_detach(tbl);
+    }
+
+    /* Recreate now if needed. */
+    if (dbentry->functions == DSM_HANDLE_INVALID &&
+        pgstat_track_functions != TRACK_FUNC_OFF)
+    {
+        dshash_table *tbl = dshash_create(area, &dsh_funcparams, 0);
+        dbentry->functions = dshash_get_hash_table_handle(tbl);
+        dshash_detach(tbl);
+    }
+
     dbentry->stat_reset_timestamp = GetCurrentTimestamp();
-    dbentry->stats_timestamp = 0;
 
-    memset(&hash_ctl, 0, sizeof(hash_ctl));
-    hash_ctl.keysize = sizeof(Oid);
-    hash_ctl.entrysize = sizeof(PgStat_StatTabEntry);
-    dbentry->tables = hash_create("Per-database table",
-                                  PGSTAT_TAB_HASH_SIZE,
-                                  &hash_ctl,
-                                  HASH_ELEM | HASH_BLOBS);
+    LWLockRelease(&dbentry->lock);
+}
 
-    hash_ctl.keysize = sizeof(Oid);
-    hash_ctl.entrysize = sizeof(PgStat_StatFuncEntry);
-    dbentry->functions = hash_create("Per-database function",
-                                     PGSTAT_FUNCTION_HASH_SIZE,
-                                     &hash_ctl,
-                                     HASH_ELEM | HASH_BLOBS);
+/*
+ * Create the filename for a DB stat file; filename is the output buffer, of
+ * length len.
+ */
+static void
+get_dbstat_filename(bool tempname, Oid databaseid, char *filename, int len)
+{
+    int            printed;
+
+    /* NB -- pgstat_reset_remove_files knows about the pattern this uses */
+    printed = snprintf(filename, len, "%s/db_%u.%s",
+                       PGSTAT_STAT_PERMANENT_DIRECTORY,
+                       databaseid,
+                       tempname ? "tmp" : "stat");
+    if (printed >= len)
+        elog(ERROR, "overlength pgstat path");
+}
+
+/* ----------
+ * pgstat_write_statsfiles() -
+ *        Write the global statistics file, as well as DB files.
+ * ----------
+ */
+void
+pgstat_write_statsfiles(void)
+{
+    dshash_seq_status hstat;
+    PgStat_StatDBEntry *dbentry;
+    FILE       *fpout;
+    int32        format_id;
+    const char *tmpfile = PGSTAT_STAT_PERMANENT_TMPFILE;
+    const char *statfile = PGSTAT_STAT_PERMANENT_FILENAME;
+    int            rc;
+
+    /* should be called from postmaster  */
+    Assert(!IsUnderPostmaster);
+
+    elog(DEBUG2, "writing stats file \"%s\"", statfile);
+
+    /*
+     * Open the statistics temp file to write out the current values.
+     */
+    fpout = AllocateFile(tmpfile, PG_BINARY_W);
+    if (fpout == NULL)
+    {
+        ereport(LOG,
+                (errcode_for_file_access(),
+                 errmsg("could not open temporary statistics file \"%s\": %m",
+                        tmpfile)));
+        return;
+    }
+
+    /*
+     * Set the timestamp of the stats file.
+     */
+    shared_globalStats->stats_timestamp = GetCurrentTimestamp();
+
+    /*
+     * Write the file header --- currently just a format ID.
+     */
+    format_id = PGSTAT_FILE_FORMAT_ID;
+    rc = fwrite(&format_id, sizeof(format_id), 1, fpout);
+    (void) rc;                    /* we'll check for error with ferror */
+
+    /*
+     * Write global stats struct
+     */
+    rc = fwrite(shared_globalStats, sizeof(*shared_globalStats), 1, fpout);
+    (void) rc;                    /* we'll check for error with ferror */
+
+    /*
+     * Write archiver stats struct
+     */
+    rc = fwrite(shared_archiverStats, sizeof(*shared_archiverStats), 1, fpout);
+    (void) rc;                    /* we'll check for error with ferror */
+
+    /*
+     * Walk through the database table.
+     */
+    dshash_seq_init(&hstat, pgStatDBHash, false, false);
+    while ((dbentry = (PgStat_StatDBEntry *) dshash_seq_next(&hstat)) != NULL)
+    {
+        /*
+         * Write out the table and function stats for this DB into the
+         * appropriate per-DB stat file, if required.
+         */
+        /* Make DB's timestamp consistent with the global stats */
+        dbentry->stats_timestamp = shared_globalStats->stats_timestamp;
+
+        pgstat_write_pgStatDBHashfile(dbentry);
+
+        /*
+         * Write out the DB entry. We don't write the tables or functions
+         * pointers, since they're of no use to any other process.
+         */
+        fputc('D', fpout);
+        rc = fwrite(dbentry,
+                    offsetof(PgStat_StatDBEntry, generation), 1, fpout);
+        (void) rc;                /* we'll check for error with ferror */
+    }
+
+    /*
+     * No more output to be done. Close the temp file and replace the old
+     * pgstat.stat with it.  The ferror() check replaces testing for error
+     * after each individual fputc or fwrite above.
+     */
+    fputc('E', fpout);
+
+    if (ferror(fpout))
+    {
+        ereport(LOG,
+                (errcode_for_file_access(),
+                 errmsg("could not write temporary statistics file \"%s\": %m",
+                        tmpfile)));
+        FreeFile(fpout);
+        unlink(tmpfile);
+    }
+    else if (FreeFile(fpout) < 0)
+    {
+        ereport(LOG,
+                (errcode_for_file_access(),
+                 errmsg("could not close temporary statistics file \"%s\": %m",
+                        tmpfile)));
+        unlink(tmpfile);
+    }
+    else if (rename(tmpfile, statfile) < 0)
+    {
+        ereport(LOG,
+                (errcode_for_file_access(),
+                 errmsg("could not rename temporary statistics file \"%s\" to \"%s\": %m",
+                        tmpfile, statfile)));
+        unlink(tmpfile);
+    }
+}
+
+/* ----------
+ * pgstat_write_pgStatDBHashfile() -
+ *        Write the stat file for a single database.
+ * ----------
+ */
+static void
+pgstat_write_pgStatDBHashfile(PgStat_StatDBEntry *dbentry)
+{
+    dshash_seq_status tstat;
+    dshash_seq_status fstat;
+    PgStat_StatTabEntry *tabentry;
+    PgStat_StatFuncEntry *funcentry;
+    FILE       *fpout;
+    int32        format_id;
+    Oid            dbid = dbentry->databaseid;
+    int            rc;
+    char        tmpfile[MAXPGPATH];
+    char        statfile[MAXPGPATH];
+    dshash_table *tbl;
+
+    get_dbstat_filename(true, dbid, tmpfile, MAXPGPATH);
+    get_dbstat_filename(false, dbid, statfile, MAXPGPATH);
+
+    elog(DEBUG2, "writing stats file \"%s\"", statfile);
+
+    /*
+     * Open the statistics temp file to write out the current values.
+     */
+    fpout = AllocateFile(tmpfile, PG_BINARY_W);
+    if (fpout == NULL)
+    {
+        ereport(LOG,
+                (errcode_for_file_access(),
+                 errmsg("could not open temporary statistics file \"%s\": %m",
+                        tmpfile)));
+        return;
+    }
+
+    /*
+     * Write the file header --- currently just a format ID.
+     */
+    format_id = PGSTAT_FILE_FORMAT_ID;
+    rc = fwrite(&format_id, sizeof(format_id), 1, fpout);
+    (void) rc;                    /* we'll check for error with ferror */
+
+    /*
+     * Walk through the database's access stats per table.
+     */
+    tbl = dshash_attach(area, &dsh_tblparams, dbentry->tables, 0);
+    dshash_seq_init(&tstat, tbl, false, false);
+    while ((tabentry = (PgStat_StatTabEntry *) dshash_seq_next(&tstat)) != NULL)
+    {
+        fputc('T', fpout);
+        rc = fwrite(tabentry, sizeof(PgStat_StatTabEntry), 1, fpout);
+        (void) rc;                /* we'll check for error with ferror */
+    }
+    dshash_detach(tbl);
+
+    /*
+     * Walk through the database's function stats table.
+     */
+    if (dbentry->functions != DSM_HANDLE_INVALID)
+    {
+        tbl = dshash_attach(area, &dsh_funcparams, dbentry->functions, 0);
+        dshash_seq_init(&fstat, tbl, false, false);
+        while ((funcentry = (PgStat_StatFuncEntry *) dshash_seq_next(&fstat)) != NULL)
+        {
+            fputc('F', fpout);
+            rc = fwrite(funcentry, sizeof(PgStat_StatFuncEntry), 1, fpout);
+            (void) rc;                /* we'll check for error with ferror */
+        }
+        dshash_detach(tbl);
+    }
+
+    /*
+     * No more output to be done. Close the temp file and replace the old
+     * pgstat.stat with it.  The ferror() check replaces testing for error
+     * after each individual fputc or fwrite above.
+     */
+    fputc('E', fpout);
+
+    if (ferror(fpout))
+    {
+        ereport(LOG,
+                (errcode_for_file_access(),
+                 errmsg("could not write temporary statistics file \"%s\": %m",
+                        tmpfile)));
+        FreeFile(fpout);
+        unlink(tmpfile);
+    }
+    else if (FreeFile(fpout) < 0)
+    {
+        ereport(LOG,
+                (errcode_for_file_access(),
+                 errmsg("could not close temporary statistics file \"%s\": %m",
+                        tmpfile)));
+        unlink(tmpfile);
+    }
+    else if (rename(tmpfile, statfile) < 0)
+    {
+        ereport(LOG,
+                (errcode_for_file_access(),
+                 errmsg("could not rename temporary statistics file \"%s\" to \"%s\": %m",
+                        tmpfile, statfile)));
+        unlink(tmpfile);
+    }
+}
+
+/* ----------
+ * pgstat_read_statsfiles() -
+ *
+ *    Reads in existing statistics collector files into the shared stats hash.
+ *
+ * ----------
+ */
+void
+pgstat_read_statsfiles(void)
+{
+    PgStat_StatDBEntry *dbentry;
+    PgStat_StatDBEntry dbbuf;
+    FILE       *fpin;
+    int32        format_id;
+    bool        found;
+    const char *statfile = PGSTAT_STAT_PERMANENT_FILENAME;
+
+    /* should be called from postmaster  */
+    Assert(!IsUnderPostmaster);
+
+    /*
+     * local cache lives in pgSharedStatsContext.
+     */
+    pgstat_setup_memcxt();
+
+    /*
+     * Create the DB hashtable and global stats area. No lock is needed since
+     * we're alone now.
+     */
+    pgstat_create_shared_stats();
+
+    /*
+     * Set the current timestamp (will be kept only in case we can't load an
+     * existing statsfile).
+     */
+    shared_globalStats->stat_reset_timestamp = GetCurrentTimestamp();
+    shared_archiverStats->stat_reset_timestamp =
+        shared_globalStats->stat_reset_timestamp;
+
+    /*
+     * Try to open the stats file. If it doesn't exist, the backends simply
+     * return zero for anything and the collector simply starts from scratch
+     * with empty counters.
+     *
+     * ENOENT is a possibility if the stats collector is not running or has
+     * not yet written the stats file the first time.  Any other failure
+     * condition is suspicious.
+     */
+    if ((fpin = AllocateFile(statfile, PG_BINARY_R)) == NULL)
+    {
+        if (errno != ENOENT)
+            ereport(LOG,
+                    (errcode_for_file_access(),
+                     errmsg("could not open statistics file \"%s\": %m",
+                            statfile)));
+        return;
+    }
+
+    /*
+     * Verify it's of the expected format.
+     */
+    if (fread(&format_id, 1, sizeof(format_id), fpin) != sizeof(format_id) ||
+        format_id != PGSTAT_FILE_FORMAT_ID)
+    {
+        ereport(LOG,
+                (errmsg("corrupted statistics file \"%s\"", statfile)));
+        goto done;
+    }
+
+    /*
+     * Read global stats struct
+     */
+    if (fread(shared_globalStats, 1, sizeof(*shared_globalStats), fpin) !=
+        sizeof(*shared_globalStats))
+    {
+        ereport(LOG,
+                (errmsg("corrupted statistics file \"%s\"", statfile)));
+        MemSet(shared_globalStats, 0, sizeof(*shared_globalStats));
+        goto done;
+    }
+
+    /*
+     * In the collector, disregard the timestamp we read from the permanent
+     * stats file; we should be willing to write a temp stats file immediately
+     * upon the first request from any backend.  This only matters if the old
+     * file's timestamp is less than PGSTAT_STAT_INTERVAL ago, but that's not
+     * an unusual scenario.
+     */
+    shared_globalStats->stats_timestamp = 0;
+
+    /*
+     * Read archiver stats struct
+     */
+    if (fread(shared_archiverStats, 1, sizeof(*shared_archiverStats), fpin) !=
+        sizeof(*shared_archiverStats))
+    {
+        ereport(LOG,
+                (errmsg("corrupted statistics file \"%s\"", statfile)));
+        MemSet(shared_archiverStats, 0, sizeof(*shared_archiverStats));
+        goto done;
+    }
+
+    /*
+     * We found an existing collector stats file. Read it and put all the
+     * hashtable entries into place.
+     */
+    for (;;)
+    {
+        switch (fgetc(fpin))
+        {
+                /*
+                 * 'D'    A PgStat_StatDBEntry struct describing a database
+                 * follows.
+                 */
+            case 'D':
+                if (fread(&dbbuf, 1, offsetof(PgStat_StatDBEntry, generation),
+                          fpin) != offsetof(PgStat_StatDBEntry, generation))
+                {
+                    ereport(LOG,
+                            (errmsg("corrupted statistics file \"%s\"",
+                                    statfile)));
+                    goto done;
+                }
+
+                /*
+                 * Add to the DB hash
+                 */
+                dbentry = (PgStat_StatDBEntry *)
+                    dshash_find_or_insert(pgStatDBHash, (void *) &dbbuf.databaseid,
+                                          &found);
+
+                /* don't allow duplicate dbentries */
+                if (found)
+                {
+                    dshash_release_lock(pgStatDBHash, dbentry);
+                    ereport(LOG,
+                            (errmsg("corrupted statistics file \"%s\"",
+                                    statfile)));
+                    goto done;
+                }
+
+                /* initialize the new shared entry */
+                init_dbentry(dbentry);
+
+                memcpy(dbentry, &dbbuf,
+                       offsetof(PgStat_StatDBEntry, generation));
+
+                /* Read the data from the database-specific file. */
+                pgstat_read_pgStatDBHashfile(dbentry);
+                dshash_release_lock(pgStatDBHash, dbentry);
+                break;
+
+            case 'E':
+                goto done;
+
+            default:
+                ereport(LOG,
+                        (errmsg("corrupted statistics file \"%s\"",
+                                statfile)));
+                goto done;
+        }
+    }
+
+done:
+    FreeFile(fpin);
+
+    elog(DEBUG2, "removing permanent stats file \"%s\"", statfile);
+    unlink(statfile);
+
+    return;
+}
+
+
+/* ----------
+ * pgstat_read_pgStatDBHashfile() -
+ *
+ *    Reads in the at-rest statistics file and create shared statistics
+ *    tables. The file is removed after reading.
+ * ----------
+ */
+static void
+pgstat_read_pgStatDBHashfile(PgStat_StatDBEntry *dbentry)
+{
+    PgStat_StatTabEntry   *tabentry;
+    PgStat_StatTabEntry        tabbuf;
+    PgStat_StatFuncEntry    funcbuf;
+    PgStat_StatFuncEntry   *funcentry;
+    dshash_table           *tabhash = NULL;
+    dshash_table           *funchash = NULL;
+    FILE       *fpin;
+    int32        format_id;
+    bool        found;
+    char        statfile[MAXPGPATH];
+
+    /* should be called from postmaster  */
+    Assert(!IsUnderPostmaster);
+
+    get_dbstat_filename(false, dbentry->databaseid, statfile, MAXPGPATH);
+
+    /*
+     * Try to open the stats file. If it doesn't exist, the backends simply
+     * return zero for anything and the collector simply starts from scratch
+     * with empty counters.
+     *
+     * ENOENT is a possibility if the stats collector is not running or has
+     * not yet written the stats file the first time.  Any other failure
+     * condition is suspicious.
+     */
+    if ((fpin = AllocateFile(statfile, PG_BINARY_R)) == NULL)
+    {
+        if (errno != ENOENT)
+            ereport(LOG,
+                    (errcode_for_file_access(),
+                     errmsg("could not open statistics file \"%s\": %m",
+                            statfile)));
+        return;
+    }
+
+    /*
+     * Verify it's of the expected format.
+     */
+    if (fread(&format_id, 1, sizeof(format_id), fpin) != sizeof(format_id) ||
+        format_id != PGSTAT_FILE_FORMAT_ID)
+    {
+        ereport(LOG,
+                (errmsg("corrupted statistics file \"%s\"", statfile)));
+        goto done;
+    }
+
+    /*
+     * We found an existing statistics file. Read it and put all the hashtable
+     * entries into place.
+     */
+    for (;;)
+    {
+        switch (fgetc(fpin))
+        {
+                /*
+                 * 'T'    A PgStat_StatTabEntry follows.
+                 */
+            case 'T':
+                if (fread(&tabbuf, 1, sizeof(PgStat_StatTabEntry),
+                          fpin) != sizeof(PgStat_StatTabEntry))
+                {
+                    ereport(LOG,
+                            (errmsg("corrupted statistics file \"%s\"",
+                                    statfile)));
+                    goto done;
+                }
+
+                if (tabhash == NULL)
+                {
+                    tabhash = dshash_create(area, &dsh_tblparams, 0);
+                    dbentry->tables =
+                        dshash_get_hash_table_handle(tabhash);
+                }
+
+                tabentry = (PgStat_StatTabEntry *)
+                    dshash_find_or_insert(tabhash,
+                                          (void *) &tabbuf.tableid, &found);
+
+                /* don't allow duplicate entries */
+                if (found)
+                {
+                    dshash_release_lock(tabhash, tabentry);
+                    ereport(LOG,
+                            (errmsg("corrupted statistics file \"%s\"",
+                                    statfile)));
+                    goto done;
+                }
+
+                memcpy(tabentry, &tabbuf, sizeof(tabbuf));
+                dshash_release_lock(tabhash, tabentry);
+                break;
+
+                /*
+                 * 'F'    A PgStat_StatFuncEntry follows.
+                 */
+            case 'F':
+                if (fread(&funcbuf, 1, sizeof(PgStat_StatFuncEntry),
+                          fpin) != sizeof(PgStat_StatFuncEntry))
+                {
+                    ereport(LOG,
+                            (errmsg("corrupted statistics file \"%s\"",
+                                    statfile)));
+                    goto done;
+                }
+
+                if (funchash == NULL)
+                {
+                    funchash = dshash_create(area, &dsh_tblparams, 0);
+                    dbentry->functions =
+                        dshash_get_hash_table_handle(funchash);
+                }
+
+                funcentry = (PgStat_StatFuncEntry *)
+                    dshash_find_or_insert(funchash,
+                                          (void *) &funcbuf.functionid, &found);
+
+                if (found)
+                {
+                    dshash_release_lock(funchash, funcentry);
+                    ereport(LOG,
+                            (errmsg("corrupted statistics file \"%s\"",
+                                    statfile)));
+                    goto done;
+                }
+
+                memcpy(funcentry, &funcbuf, sizeof(funcbuf));
+                dshash_release_lock(funchash, funcentry);
+                break;
+
+                /*
+                 * 'E'    The EOF marker of a complete stats file.
+                 */
+            case 'E':
+                goto done;
+
+            default:
+                ereport(LOG,
+                        (errmsg("corrupted statistics file \"%s\"",
+                                statfile)));
+                goto done;
+        }
+    }
+
+done:
+    if (tabhash)
+        dshash_detach(tabhash);
+    if (funchash)
+        dshash_detach(funchash);
+
+    FreeFile(fpin);
+
+    elog(DEBUG2, "removing permanent stats file \"%s\"", statfile);
+    unlink(statfile);
+}
+
+/* ----------
+ * pgstat_setup_memcxt() -
+ *
+ *    Create pgSharedStatsContext, if not already done.
+ * ----------
+ */
+static void
+pgstat_setup_memcxt(void)
+{
+    if (!pgStatLocalContext)
+        pgStatLocalContext =
+            AllocSetContextCreate(TopMemoryContext,
+                                  "Backend statistics snapshot",
+                                  ALLOCSET_SMALL_SIZES);
+    if (!pgSharedStatsContext)
+        pgSharedStatsContext =
+            AllocSetContextCreate(TopMemoryContext,
+                                  "Shared activity statistics",
+                                  ALLOCSET_SMALL_SIZES);
+}
+
+/* ----------
+ * pgstat_clear_snapshot() -
+ *
+ *    Discard any data collected in the current transaction.  Any subsequent
+ *    request will cause new snapshots to be read.
+ *
+ *    This is also invoked during transaction commit or abort to discard
+ *    the no-longer-wanted snapshot.
+ * ----------
+ */
+void
+pgstat_clear_snapshot(void)
+{
+    /* Release memory, if any was allocated */
+    if (pgStatLocalContext)
+    {
+        MemoryContextDelete(pgStatLocalContext);
+
+        /* Reset variables */
+        pgStatLocalContext = NULL;
+        localBackendStatusTable = NULL;
+        localNumBackends = 0;
+    }
+
+    if (pgStatSnapshotContext)
+    {
+        MemoryContextReset(pgStatSnapshotContext);
+
+        /* mark as the resource are not allocated */
+        snapshot_globalStats = NULL;
+        snapshot_archiverStats = NULL;
+        pgStatDBEntrySnapshot = NULL;
+    }
+}
+
+static bool
+pgstat_update_tabentry(dshash_table *tabhash, PgStat_TableStatus *stat,
+                       bool nowait)
+{
+    PgStat_StatTabEntry *tabentry;
+    bool    found;
+
+    if (tabhash == NULL)
+        return false;
+
+    tabentry = (PgStat_StatTabEntry *)
+        dshash_find_or_insert_extended(tabhash, (void *) &(stat->t_id),
+                                       &found, nowait);
+
+    /* failed to acquire lock */
+    if (tabentry == NULL)
+        return false;
+
+    if (!found)
+    {
+        /*
+         * If it's a new table entry, initialize counters to the values we
+         * just got.
+         */
+        tabentry->numscans = stat->t_counts.t_numscans;
+        tabentry->tuples_returned = stat->t_counts.t_tuples_returned;
+        tabentry->tuples_fetched = stat->t_counts.t_tuples_fetched;
+        tabentry->tuples_inserted = stat->t_counts.t_tuples_inserted;
+        tabentry->tuples_updated = stat->t_counts.t_tuples_updated;
+        tabentry->tuples_deleted = stat->t_counts.t_tuples_deleted;
+        tabentry->tuples_hot_updated = stat->t_counts.t_tuples_hot_updated;
+        tabentry->n_live_tuples = stat->t_counts.t_delta_live_tuples;
+        tabentry->n_dead_tuples = stat->t_counts.t_delta_dead_tuples;
+        tabentry->changes_since_analyze = stat->t_counts.t_changed_tuples;
+        tabentry->blocks_fetched = stat->t_counts.t_blocks_fetched;
+        tabentry->blocks_hit = stat->t_counts.t_blocks_hit;
+
+        tabentry->vacuum_timestamp = 0;
+        tabentry->vacuum_count = 0;
+        tabentry->autovac_vacuum_timestamp = 0;
+        tabentry->autovac_vacuum_count = 0;
+        tabentry->analyze_timestamp = 0;
+        tabentry->analyze_count = 0;
+        tabentry->autovac_analyze_timestamp = 0;
+        tabentry->autovac_analyze_count = 0;
+    }
+    else
+    {
+        /*
+         * Otherwise add the values to the existing entry.
+         */
+        tabentry->numscans += stat->t_counts.t_numscans;
+        tabentry->tuples_returned += stat->t_counts.t_tuples_returned;
+        tabentry->tuples_fetched += stat->t_counts.t_tuples_fetched;
+        tabentry->tuples_inserted += stat->t_counts.t_tuples_inserted;
+        tabentry->tuples_updated += stat->t_counts.t_tuples_updated;
+        tabentry->tuples_deleted += stat->t_counts.t_tuples_deleted;
+        tabentry->tuples_hot_updated += stat->t_counts.t_tuples_hot_updated;
+        /* If table was truncated, first reset the live/dead counters */
+        if (stat->t_counts.t_truncated)
+        {
+            tabentry->n_live_tuples = 0;
+            tabentry->n_dead_tuples = 0;
+        }
+        tabentry->n_live_tuples += stat->t_counts.t_delta_live_tuples;
+        tabentry->n_dead_tuples += stat->t_counts.t_delta_dead_tuples;
+        tabentry->changes_since_analyze += stat->t_counts.t_changed_tuples;
+        tabentry->blocks_fetched += stat->t_counts.t_blocks_fetched;
+        tabentry->blocks_hit += stat->t_counts.t_blocks_hit;
+    }
+
+    /* Clamp n_live_tuples in case of negative delta_live_tuples */
+    tabentry->n_live_tuples = Max(tabentry->n_live_tuples, 0);
+    /* Likewise for n_dead_tuples */
+    tabentry->n_dead_tuples = Max(tabentry->n_dead_tuples, 0);
+
+    dshash_release_lock(tabhash, tabentry);
+
+    return true;
+}
+
+static void
+pgstat_update_dbentry(PgStat_StatDBEntry *dbentry, PgStat_TableStatus *stat)
+{
+    /*
+     * Add per-table stats to the per-database entry, too.
+     */
+    LWLockAcquire(&dbentry->lock, LW_EXCLUSIVE);
+    dbentry->n_tuples_returned += stat->t_counts.t_tuples_returned;
+    dbentry->n_tuples_fetched += stat->t_counts.t_tuples_fetched;
+    dbentry->n_tuples_inserted += stat->t_counts.t_tuples_inserted;
+    dbentry->n_tuples_updated += stat->t_counts.t_tuples_updated;
+    dbentry->n_tuples_deleted += stat->t_counts.t_tuples_deleted;
+    dbentry->n_blocks_fetched += stat->t_counts.t_blocks_fetched;
+    dbentry->n_blocks_hit += stat->t_counts.t_blocks_hit;
+    LWLockRelease(&dbentry->lock);
 }
 
 /*
@@ -4588,47 +5522,79 @@ reset_dbentry_counters(PgStat_StatDBEntry *dbentry)
  * Else, return NULL.
  */
 static PgStat_StatDBEntry *
-pgstat_get_db_entry(Oid databaseid, bool create)
+pgstat_get_db_entry(Oid databaseid, int op,    PgStat_TableLookupState *status)
 {
     PgStat_StatDBEntry *result;
-    bool        found;
-    HASHACTION    action = (create ? HASH_ENTER : HASH_FIND);
+    bool        nowait = ((op & PGSTAT_FETCH_NOWAIT) != 0);
+    bool        lock_acquired = true;
+    bool        found = true;
 
-    /* Lookup or create the hash table entry for this database */
-    result = (PgStat_StatDBEntry *) hash_search(pgStatDBHash,
-                                                &databaseid,
-                                                action, &found);
-
-    if (!create && !found)
+    if (!IsUnderPostmaster)
         return NULL;
 
-    /*
-     * If not found, initialize the new one.  This creates empty hash tables
-     * for tables and functions, too.
-     */
-    if (!found)
-        reset_dbentry_counters(result);
+    Assert(pgStatDBHash);
+
+    /* Lookup or create the hash table entry for this database */
+    if (op & PGSTAT_FETCH_EXCLUSIVE)
+    {
+        result = (PgStat_StatDBEntry *)
+            dshash_find_or_insert_extended(pgStatDBHash, &databaseid,
+                                           &found, nowait);
+        if (result == NULL)
+            lock_acquired = false;
+        else if (!found)
+        {
+            /*
+             * If not found, initialize the new one.  This creates empty hash
+             * tables hash, too.
+             */
+            init_dbentry(result);
+            reset_dbentry_counters(result);
+        }
+    }
+    else
+    {
+        result = (PgStat_StatDBEntry *)
+            dshash_find_extended(pgStatDBHash, &databaseid, true, nowait,
+                                 nowait ? &lock_acquired : NULL);
+        if (result == NULL)
+            found = false;
+    }
+
+    /* Set return status if requested */
+    if (status)
+    {
+        if (!lock_acquired)
+        {
+            Assert(nowait);
+            *status = PGSTAT_ENTRY_LOCK_FAILED;
+        }
+        else if (!found)
+            *status = PGSTAT_ENTRY_NOT_FOUND;
+        else
+            *status = PGSTAT_ENTRY_FOUND;
+    }
 
     return result;
 }
 
-
 /*
  * Lookup the hash table entry for the specified table. If no hash
  * table entry exists, initialize it, if the create parameter is true.
  * Else, return NULL.
  */
 static PgStat_StatTabEntry *
-pgstat_get_tab_entry(PgStat_StatDBEntry *dbentry, Oid tableoid, bool create)
+pgstat_get_tab_entry(dshash_table *table, Oid tableoid, bool create)
 {
     PgStat_StatTabEntry *result;
     bool        found;
-    HASHACTION    action = (create ? HASH_ENTER : HASH_FIND);
 
     /* Lookup or create the hash table entry for this table */
-    result = (PgStat_StatTabEntry *) hash_search(dbentry->tables,
-                                                 &tableoid,
-                                                 action, &found);
+    if (create)
+        result = (PgStat_StatTabEntry *)
+            dshash_find_or_insert(table, &tableoid, &found);
+    else
+        result = (PgStat_StatTabEntry *) dshash_find(table, &tableoid, false);
 
     if (!create && !found)
         return NULL;
@@ -4661,1685 +5627,6 @@ pgstat_get_tab_entry(PgStat_StatDBEntry *dbentry, Oid tableoid, bool create)
     return result;
 }
 
-
-/* ----------
- * pgstat_write_statsfiles() -
- *        Write the global statistics file, as well as requested DB files.
- *
- *    'permanent' specifies writing to the permanent files not temporary ones.
- *    When true (happens only when the collector is shutting down), also remove
- *    the temporary files so that backends starting up under a new postmaster
- *    can't read old data before the new collector is ready.
- *
- *    When 'allDbs' is false, only the requested databases (listed in
- *    pending_write_requests) will be written; otherwise, all databases
- *    will be written.
- * ----------
- */
-static void
-pgstat_write_statsfiles(bool permanent, bool allDbs)
-{
-    HASH_SEQ_STATUS hstat;
-    PgStat_StatDBEntry *dbentry;
-    FILE       *fpout;
-    int32        format_id;
-    const char *tmpfile = permanent ? PGSTAT_STAT_PERMANENT_TMPFILE : pgstat_stat_tmpname;
-    const char *statfile = permanent ? PGSTAT_STAT_PERMANENT_FILENAME : pgstat_stat_filename;
-    int            rc;
-
-    elog(DEBUG2, "writing stats file \"%s\"", statfile);
-
-    /*
-     * Open the statistics temp file to write out the current values.
-     */
-    fpout = AllocateFile(tmpfile, PG_BINARY_W);
-    if (fpout == NULL)
-    {
-        ereport(LOG,
-                (errcode_for_file_access(),
-                 errmsg("could not open temporary statistics file \"%s\": %m",
-                        tmpfile)));
-        return;
-    }
-
-    /*
-     * Set the timestamp of the stats file.
-     */
-    globalStats.stats_timestamp = GetCurrentTimestamp();
-
-    /*
-     * Write the file header --- currently just a format ID.
-     */
-    format_id = PGSTAT_FILE_FORMAT_ID;
-    rc = fwrite(&format_id, sizeof(format_id), 1, fpout);
-    (void) rc;                    /* we'll check for error with ferror */
-
-    /*
-     * Write global stats struct
-     */
-    rc = fwrite(&globalStats, sizeof(globalStats), 1, fpout);
-    (void) rc;                    /* we'll check for error with ferror */
-
-    /*
-     * Write archiver stats struct
-     */
-    rc = fwrite(&archiverStats, sizeof(archiverStats), 1, fpout);
-    (void) rc;                    /* we'll check for error with ferror */
-
-    /*
-     * Walk through the database table.
-     */
-    hash_seq_init(&hstat, pgStatDBHash);
-    while ((dbentry = (PgStat_StatDBEntry *) hash_seq_search(&hstat)) != NULL)
-    {
-        /*
-         * Write out the table and function stats for this DB into the
-         * appropriate per-DB stat file, if required.
-         */
-        if (allDbs || pgstat_db_requested(dbentry->databaseid))
-        {
-            /* Make DB's timestamp consistent with the global stats */
-            dbentry->stats_timestamp = globalStats.stats_timestamp;
-
-            pgstat_write_db_statsfile(dbentry, permanent);
-        }
-
-        /*
-         * Write out the DB entry. We don't write the tables or functions
-         * pointers, since they're of no use to any other process.
-         */
-        fputc('D', fpout);
-        rc = fwrite(dbentry, offsetof(PgStat_StatDBEntry, tables), 1, fpout);
-        (void) rc;                /* we'll check for error with ferror */
-    }
-
-    /*
-     * No more output to be done. Close the temp file and replace the old
-     * pgstat.stat with it.  The ferror() check replaces testing for error
-     * after each individual fputc or fwrite above.
-     */
-    fputc('E', fpout);
-
-    if (ferror(fpout))
-    {
-        ereport(LOG,
-                (errcode_for_file_access(),
-                 errmsg("could not write temporary statistics file \"%s\": %m",
-                        tmpfile)));
-        FreeFile(fpout);
-        unlink(tmpfile);
-    }
-    else if (FreeFile(fpout) < 0)
-    {
-        ereport(LOG,
-                (errcode_for_file_access(),
-                 errmsg("could not close temporary statistics file \"%s\": %m",
-                        tmpfile)));
-        unlink(tmpfile);
-    }
-    else if (rename(tmpfile, statfile) < 0)
-    {
-        ereport(LOG,
-                (errcode_for_file_access(),
-                 errmsg("could not rename temporary statistics file \"%s\" to \"%s\": %m",
-                        tmpfile, statfile)));
-        unlink(tmpfile);
-    }
-
-    if (permanent)
-        unlink(pgstat_stat_filename);
-
-    /*
-     * Now throw away the list of requests.  Note that requests sent after we
-     * started the write are still waiting on the network socket.
-     */
-    list_free(pending_write_requests);
-    pending_write_requests = NIL;
-}
-
-/*
- * return the filename for a DB stat file; filename is the output buffer,
- * of length len.
- */
-static void
-get_dbstat_filename(bool permanent, bool tempname, Oid databaseid,
-                    char *filename, int len)
-{
-    int            printed;
-
-    /* NB -- pgstat_reset_remove_files knows about the pattern this uses */
-    printed = snprintf(filename, len, "%s/db_%u.%s",
-                       permanent ? PGSTAT_STAT_PERMANENT_DIRECTORY :
-                       pgstat_stat_directory,
-                       databaseid,
-                       tempname ? "tmp" : "stat");
-    if (printed >= len)
-        elog(ERROR, "overlength pgstat path");
-}
-
-/* ----------
- * pgstat_write_db_statsfile() -
- *        Write the stat file for a single database.
- *
- *    If writing to the permanent file (happens when the collector is
- *    shutting down only), remove the temporary file so that backends
- *    starting up under a new postmaster can't read the old data before
- *    the new collector is ready.
- * ----------
- */
-static void
-pgstat_write_db_statsfile(PgStat_StatDBEntry *dbentry, bool permanent)
-{
-    HASH_SEQ_STATUS tstat;
-    HASH_SEQ_STATUS fstat;
-    PgStat_StatTabEntry *tabentry;
-    PgStat_StatFuncEntry *funcentry;
-    FILE       *fpout;
-    int32        format_id;
-    Oid            dbid = dbentry->databaseid;
-    int            rc;
-    char        tmpfile[MAXPGPATH];
-    char        statfile[MAXPGPATH];
-
-    get_dbstat_filename(permanent, true, dbid, tmpfile, MAXPGPATH);
-    get_dbstat_filename(permanent, false, dbid, statfile, MAXPGPATH);
-
-    elog(DEBUG2, "writing stats file \"%s\"", statfile);
-
-    /*
-     * Open the statistics temp file to write out the current values.
-     */
-    fpout = AllocateFile(tmpfile, PG_BINARY_W);
-    if (fpout == NULL)
-    {
-        ereport(LOG,
-                (errcode_for_file_access(),
-                 errmsg("could not open temporary statistics file \"%s\": %m",
-                        tmpfile)));
-        return;
-    }
-
-    /*
-     * Write the file header --- currently just a format ID.
-     */
-    format_id = PGSTAT_FILE_FORMAT_ID;
-    rc = fwrite(&format_id, sizeof(format_id), 1, fpout);
-    (void) rc;                    /* we'll check for error with ferror */
-
-    /*
-     * Walk through the database's access stats per table.
-     */
-    hash_seq_init(&tstat, dbentry->tables);
-    while ((tabentry = (PgStat_StatTabEntry *) hash_seq_search(&tstat)) != NULL)
-    {
-        fputc('T', fpout);
-        rc = fwrite(tabentry, sizeof(PgStat_StatTabEntry), 1, fpout);
-        (void) rc;                /* we'll check for error with ferror */
-    }
-
-    /*
-     * Walk through the database's function stats table.
-     */
-    hash_seq_init(&fstat, dbentry->functions);
-    while ((funcentry = (PgStat_StatFuncEntry *) hash_seq_search(&fstat)) != NULL)
-    {
-        fputc('F', fpout);
-        rc = fwrite(funcentry, sizeof(PgStat_StatFuncEntry), 1, fpout);
-        (void) rc;                /* we'll check for error with ferror */
-    }
-
-    /*
-     * No more output to be done. Close the temp file and replace the old
-     * pgstat.stat with it.  The ferror() check replaces testing for error
-     * after each individual fputc or fwrite above.
-     */
-    fputc('E', fpout);
-
-    if (ferror(fpout))
-    {
-        ereport(LOG,
-                (errcode_for_file_access(),
-                 errmsg("could not write temporary statistics file \"%s\": %m",
-                        tmpfile)));
-        FreeFile(fpout);
-        unlink(tmpfile);
-    }
-    else if (FreeFile(fpout) < 0)
-    {
-        ereport(LOG,
-                (errcode_for_file_access(),
-                 errmsg("could not close temporary statistics file \"%s\": %m",
-                        tmpfile)));
-        unlink(tmpfile);
-    }
-    else if (rename(tmpfile, statfile) < 0)
-    {
-        ereport(LOG,
-                (errcode_for_file_access(),
-                 errmsg("could not rename temporary statistics file \"%s\" to \"%s\": %m",
-                        tmpfile, statfile)));
-        unlink(tmpfile);
-    }
-
-    if (permanent)
-    {
-        get_dbstat_filename(false, false, dbid, statfile, MAXPGPATH);
-
-        elog(DEBUG2, "removing temporary stats file \"%s\"", statfile);
-        unlink(statfile);
-    }
-}
-
-/* ----------
- * pgstat_read_statsfiles() -
- *
- *    Reads in some existing statistics collector files and returns the
- *    databases hash table that is the top level of the data.
- *
- *    If 'onlydb' is not InvalidOid, it means we only want data for that DB
- *    plus the shared catalogs ("DB 0").  We'll still populate the DB hash
- *    table for all databases, but we don't bother even creating table/function
- *    hash tables for other databases.
- *
- *    'permanent' specifies reading from the permanent files not temporary ones.
- *    When true (happens only when the collector is starting up), remove the
- *    files after reading; the in-memory status is now authoritative, and the
- *    files would be out of date in case somebody else reads them.
- *
- *    If a 'deep' read is requested, table/function stats are read, otherwise
- *    the table/function hash tables remain empty.
- * ----------
- */
-static HTAB *
-pgstat_read_statsfiles(Oid onlydb, bool permanent, bool deep)
-{
-    PgStat_StatDBEntry *dbentry;
-    PgStat_StatDBEntry dbbuf;
-    HASHCTL        hash_ctl;
-    HTAB       *dbhash;
-    FILE       *fpin;
-    int32        format_id;
-    bool        found;
-    const char *statfile = permanent ? PGSTAT_STAT_PERMANENT_FILENAME : pgstat_stat_filename;
-
-    /*
-     * The tables will live in pgStatLocalContext.
-     */
-    pgstat_setup_memcxt();
-
-    /*
-     * Create the DB hashtable
-     */
-    memset(&hash_ctl, 0, sizeof(hash_ctl));
-    hash_ctl.keysize = sizeof(Oid);
-    hash_ctl.entrysize = sizeof(PgStat_StatDBEntry);
-    hash_ctl.hcxt = pgStatLocalContext;
-    dbhash = hash_create("Databases hash", PGSTAT_DB_HASH_SIZE, &hash_ctl,
-                         HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
-
-    /*
-     * Clear out global and archiver statistics so they start from zero in
-     * case we can't load an existing statsfile.
-     */
-    memset(&globalStats, 0, sizeof(globalStats));
-    memset(&archiverStats, 0, sizeof(archiverStats));
-
-    /*
-     * Set the current timestamp (will be kept only in case we can't load an
-     * existing statsfile).
-     */
-    globalStats.stat_reset_timestamp = GetCurrentTimestamp();
-    archiverStats.stat_reset_timestamp = globalStats.stat_reset_timestamp;
-
-    /*
-     * Try to open the stats file. If it doesn't exist, the backends simply
-     * return zero for anything and the collector simply starts from scratch
-     * with empty counters.
-     *
-     * ENOENT is a possibility if the stats collector is not running or has
-     * not yet written the stats file the first time.  Any other failure
-     * condition is suspicious.
-     */
-    if ((fpin = AllocateFile(statfile, PG_BINARY_R)) == NULL)
-    {
-        if (errno != ENOENT)
-            ereport(pgStatRunningInCollector ? LOG : WARNING,
-                    (errcode_for_file_access(),
-                     errmsg("could not open statistics file \"%s\": %m",
-                            statfile)));
-        return dbhash;
-    }
-
-    /*
-     * Verify it's of the expected format.
-     */
-    if (fread(&format_id, 1, sizeof(format_id), fpin) != sizeof(format_id) ||
-        format_id != PGSTAT_FILE_FORMAT_ID)
-    {
-        ereport(pgStatRunningInCollector ? LOG : WARNING,
-                (errmsg("corrupted statistics file \"%s\"", statfile)));
-        goto done;
-    }
-
-    /*
-     * Read global stats struct
-     */
-    if (fread(&globalStats, 1, sizeof(globalStats), fpin) != sizeof(globalStats))
-    {
-        ereport(pgStatRunningInCollector ? LOG : WARNING,
-                (errmsg("corrupted statistics file \"%s\"", statfile)));
-        memset(&globalStats, 0, sizeof(globalStats));
-        goto done;
-    }
-
-    /*
-     * In the collector, disregard the timestamp we read from the permanent
-     * stats file; we should be willing to write a temp stats file immediately
-     * upon the first request from any backend.  This only matters if the old
-     * file's timestamp is less than PGSTAT_STAT_INTERVAL ago, but that's not
-     * an unusual scenario.
-     */
-    if (pgStatRunningInCollector)
-        globalStats.stats_timestamp = 0;
-
-    /*
-     * Read archiver stats struct
-     */
-    if (fread(&archiverStats, 1, sizeof(archiverStats), fpin) != sizeof(archiverStats))
-    {
-        ereport(pgStatRunningInCollector ? LOG : WARNING,
-                (errmsg("corrupted statistics file \"%s\"", statfile)));
-        memset(&archiverStats, 0, sizeof(archiverStats));
-        goto done;
-    }
-
-    /*
-     * We found an existing collector stats file. Read it and put all the
-     * hashtable entries into place.
-     */
-    for (;;)
-    {
-        switch (fgetc(fpin))
-        {
-                /*
-                 * 'D'    A PgStat_StatDBEntry struct describing a database
-                 * follows.
-                 */
-            case 'D':
-                if (fread(&dbbuf, 1, offsetof(PgStat_StatDBEntry, tables),
-                          fpin) != offsetof(PgStat_StatDBEntry, tables))
-                {
-                    ereport(pgStatRunningInCollector ? LOG : WARNING,
-                            (errmsg("corrupted statistics file \"%s\"",
-                                    statfile)));
-                    goto done;
-                }
-
-                /*
-                 * Add to the DB hash
-                 */
-                dbentry = (PgStat_StatDBEntry *) hash_search(dbhash,
-                                                             (void *) &dbbuf.databaseid,
-                                                             HASH_ENTER,
-                                                             &found);
-                if (found)
-                {
-                    ereport(pgStatRunningInCollector ? LOG : WARNING,
-                            (errmsg("corrupted statistics file \"%s\"",
-                                    statfile)));
-                    goto done;
-                }
-
-                memcpy(dbentry, &dbbuf, sizeof(PgStat_StatDBEntry));
-                dbentry->tables = NULL;
-                dbentry->functions = NULL;
-
-                /*
-                 * In the collector, disregard the timestamp we read from the
-                 * permanent stats file; we should be willing to write a temp
-                 * stats file immediately upon the first request from any
-                 * backend.
-                 */
-                if (pgStatRunningInCollector)
-                    dbentry->stats_timestamp = 0;
-
-                /*
-                 * Don't create tables/functions hashtables for uninteresting
-                 * databases.
-                 */
-                if (onlydb != InvalidOid)
-                {
-                    if (dbbuf.databaseid != onlydb &&
-                        dbbuf.databaseid != InvalidOid)
-                        break;
-                }
-
-                memset(&hash_ctl, 0, sizeof(hash_ctl));
-                hash_ctl.keysize = sizeof(Oid);
-                hash_ctl.entrysize = sizeof(PgStat_StatTabEntry);
-                hash_ctl.hcxt = pgStatLocalContext;
-                dbentry->tables = hash_create("Per-database table",
-                                              PGSTAT_TAB_HASH_SIZE,
-                                              &hash_ctl,
-                                              HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
-
-                hash_ctl.keysize = sizeof(Oid);
-                hash_ctl.entrysize = sizeof(PgStat_StatFuncEntry);
-                hash_ctl.hcxt = pgStatLocalContext;
-                dbentry->functions = hash_create("Per-database function",
-                                                 PGSTAT_FUNCTION_HASH_SIZE,
-                                                 &hash_ctl,
-                                                 HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
-
-                /*
-                 * If requested, read the data from the database-specific
-                 * file.  Otherwise we just leave the hashtables empty.
-                 */
-                if (deep)
-                    pgstat_read_db_statsfile(dbentry->databaseid,
-                                             dbentry->tables,
-                                             dbentry->functions,
-                                             permanent);
-
-                break;
-
-            case 'E':
-                goto done;
-
-            default:
-                ereport(pgStatRunningInCollector ? LOG : WARNING,
-                        (errmsg("corrupted statistics file \"%s\"",
-                                statfile)));
-                goto done;
-        }
-    }
-
-done:
-    FreeFile(fpin);
-
-    /* If requested to read the permanent file, also get rid of it. */
-    if (permanent)
-    {
-        elog(DEBUG2, "removing permanent stats file \"%s\"", statfile);
-        unlink(statfile);
-    }
-
-    return dbhash;
-}
-
-
-/* ----------
- * pgstat_read_db_statsfile() -
- *
- *    Reads in the existing statistics collector file for the given database,
- *    filling the passed-in tables and functions hash tables.
- *
- *    As in pgstat_read_statsfiles, if the permanent file is requested, it is
- *    removed after reading.
- *
- *    Note: this code has the ability to skip storing per-table or per-function
- *    data, if NULL is passed for the corresponding hashtable.  That's not used
- *    at the moment though.
- * ----------
- */
-static void
-pgstat_read_db_statsfile(Oid databaseid, HTAB *tabhash, HTAB *funchash,
-                         bool permanent)
-{
-    PgStat_StatTabEntry *tabentry;
-    PgStat_StatTabEntry tabbuf;
-    PgStat_StatFuncEntry funcbuf;
-    PgStat_StatFuncEntry *funcentry;
-    FILE       *fpin;
-    int32        format_id;
-    bool        found;
-    char        statfile[MAXPGPATH];
-
-    get_dbstat_filename(permanent, false, databaseid, statfile, MAXPGPATH);
-
-    /*
-     * Try to open the stats file. If it doesn't exist, the backends simply
-     * return zero for anything and the collector simply starts from scratch
-     * with empty counters.
-     *
-     * ENOENT is a possibility if the stats collector is not running or has
-     * not yet written the stats file the first time.  Any other failure
-     * condition is suspicious.
-     */
-    if ((fpin = AllocateFile(statfile, PG_BINARY_R)) == NULL)
-    {
-        if (errno != ENOENT)
-            ereport(pgStatRunningInCollector ? LOG : WARNING,
-                    (errcode_for_file_access(),
-                     errmsg("could not open statistics file \"%s\": %m",
-                            statfile)));
-        return;
-    }
-
-    /*
-     * Verify it's of the expected format.
-     */
-    if (fread(&format_id, 1, sizeof(format_id), fpin) != sizeof(format_id) ||
-        format_id != PGSTAT_FILE_FORMAT_ID)
-    {
-        ereport(pgStatRunningInCollector ? LOG : WARNING,
-                (errmsg("corrupted statistics file \"%s\"", statfile)));
-        goto done;
-    }
-
-    /*
-     * We found an existing collector stats file. Read it and put all the
-     * hashtable entries into place.
-     */
-    for (;;)
-    {
-        switch (fgetc(fpin))
-        {
-                /*
-                 * 'T'    A PgStat_StatTabEntry follows.
-                 */
-            case 'T':
-                if (fread(&tabbuf, 1, sizeof(PgStat_StatTabEntry),
-                          fpin) != sizeof(PgStat_StatTabEntry))
-                {
-                    ereport(pgStatRunningInCollector ? LOG : WARNING,
-                            (errmsg("corrupted statistics file \"%s\"",
-                                    statfile)));
-                    goto done;
-                }
-
-                /*
-                 * Skip if table data not wanted.
-                 */
-                if (tabhash == NULL)
-                    break;
-
-                tabentry = (PgStat_StatTabEntry *) hash_search(tabhash,
-                                                               (void *) &tabbuf.tableid,
-                                                               HASH_ENTER, &found);
-
-                if (found)
-                {
-                    ereport(pgStatRunningInCollector ? LOG : WARNING,
-                            (errmsg("corrupted statistics file \"%s\"",
-                                    statfile)));
-                    goto done;
-                }
-
-                memcpy(tabentry, &tabbuf, sizeof(tabbuf));
-                break;
-
-                /*
-                 * 'F'    A PgStat_StatFuncEntry follows.
-                 */
-            case 'F':
-                if (fread(&funcbuf, 1, sizeof(PgStat_StatFuncEntry),
-                          fpin) != sizeof(PgStat_StatFuncEntry))
-                {
-                    ereport(pgStatRunningInCollector ? LOG : WARNING,
-                            (errmsg("corrupted statistics file \"%s\"",
-                                    statfile)));
-                    goto done;
-                }
-
-                /*
-                 * Skip if function data not wanted.
-                 */
-                if (funchash == NULL)
-                    break;
-
-                funcentry = (PgStat_StatFuncEntry *) hash_search(funchash,
-                                                                 (void *) &funcbuf.functionid,
-                                                                 HASH_ENTER, &found);
-
-                if (found)
-                {
-                    ereport(pgStatRunningInCollector ? LOG : WARNING,
-                            (errmsg("corrupted statistics file \"%s\"",
-                                    statfile)));
-                    goto done;
-                }
-
-                memcpy(funcentry, &funcbuf, sizeof(funcbuf));
-                break;
-
-                /*
-                 * 'E'    The EOF marker of a complete stats file.
-                 */
-            case 'E':
-                goto done;
-
-            default:
-                ereport(pgStatRunningInCollector ? LOG : WARNING,
-                        (errmsg("corrupted statistics file \"%s\"",
-                                statfile)));
-                goto done;
-        }
-    }
-
-done:
-    FreeFile(fpin);
-
-    if (permanent)
-    {
-        elog(DEBUG2, "removing permanent stats file \"%s\"", statfile);
-        unlink(statfile);
-    }
-}
-
-/* ----------
- * pgstat_read_db_statsfile_timestamp() -
- *
- *    Attempt to determine the timestamp of the last db statfile write.
- *    Returns true if successful; the timestamp is stored in *ts.
- *
- *    This needs to be careful about handling databases for which no stats file
- *    exists, such as databases without a stat entry or those not yet written:
- *
- *    - if there's a database entry in the global file, return the corresponding
- *    stats_timestamp value.
- *
- *    - if there's no db stat entry (e.g. for a new or inactive database),
- *    there's no stats_timestamp value, but also nothing to write so we return
- *    the timestamp of the global statfile.
- * ----------
- */
-static bool
-pgstat_read_db_statsfile_timestamp(Oid databaseid, bool permanent,
-                                   TimestampTz *ts)
-{
-    PgStat_StatDBEntry dbentry;
-    PgStat_GlobalStats myGlobalStats;
-    PgStat_ArchiverStats myArchiverStats;
-    FILE       *fpin;
-    int32        format_id;
-    const char *statfile = permanent ? PGSTAT_STAT_PERMANENT_FILENAME : pgstat_stat_filename;
-
-    /*
-     * Try to open the stats file.  As above, anything but ENOENT is worthy of
-     * complaining about.
-     */
-    if ((fpin = AllocateFile(statfile, PG_BINARY_R)) == NULL)
-    {
-        if (errno != ENOENT)
-            ereport(pgStatRunningInCollector ? LOG : WARNING,
-                    (errcode_for_file_access(),
-                     errmsg("could not open statistics file \"%s\": %m",
-                            statfile)));
-        return false;
-    }
-
-    /*
-     * Verify it's of the expected format.
-     */
-    if (fread(&format_id, 1, sizeof(format_id), fpin) != sizeof(format_id) ||
-        format_id != PGSTAT_FILE_FORMAT_ID)
-    {
-        ereport(pgStatRunningInCollector ? LOG : WARNING,
-                (errmsg("corrupted statistics file \"%s\"", statfile)));
-        FreeFile(fpin);
-        return false;
-    }
-
-    /*
-     * Read global stats struct
-     */
-    if (fread(&myGlobalStats, 1, sizeof(myGlobalStats),
-              fpin) != sizeof(myGlobalStats))
-    {
-        ereport(pgStatRunningInCollector ? LOG : WARNING,
-                (errmsg("corrupted statistics file \"%s\"", statfile)));
-        FreeFile(fpin);
-        return false;
-    }
-
-    /*
-     * Read archiver stats struct
-     */
-    if (fread(&myArchiverStats, 1, sizeof(myArchiverStats),
-              fpin) != sizeof(myArchiverStats))
-    {
-        ereport(pgStatRunningInCollector ? LOG : WARNING,
-                (errmsg("corrupted statistics file \"%s\"", statfile)));
-        FreeFile(fpin);
-        return false;
-    }
-
-    /* By default, we're going to return the timestamp of the global file. */
-    *ts = myGlobalStats.stats_timestamp;
-
-    /*
-     * We found an existing collector stats file.  Read it and look for a
-     * record for the requested database.  If found, use its timestamp.
-     */
-    for (;;)
-    {
-        switch (fgetc(fpin))
-        {
-                /*
-                 * 'D'    A PgStat_StatDBEntry struct describing a database
-                 * follows.
-                 */
-            case 'D':
-                if (fread(&dbentry, 1, offsetof(PgStat_StatDBEntry, tables),
-                          fpin) != offsetof(PgStat_StatDBEntry, tables))
-                {
-                    ereport(pgStatRunningInCollector ? LOG : WARNING,
-                            (errmsg("corrupted statistics file \"%s\"",
-                                    statfile)));
-                    goto done;
-                }
-
-                /*
-                 * If this is the DB we're looking for, save its timestamp and
-                 * we're done.
-                 */
-                if (dbentry.databaseid == databaseid)
-                {
-                    *ts = dbentry.stats_timestamp;
-                    goto done;
-                }
-
-                break;
-
-            case 'E':
-                goto done;
-
-            default:
-                ereport(pgStatRunningInCollector ? LOG : WARNING,
-                        (errmsg("corrupted statistics file \"%s\"",
-                                statfile)));
-                goto done;
-        }
-    }
-
-done:
-    FreeFile(fpin);
-    return true;
-}
-
-/*
- * If not already done, read the statistics collector stats file into
- * some hash tables.  The results will be kept until pgstat_clear_snapshot()
- * is called (typically, at end of transaction).
- */
-static void
-backend_read_statsfile(void)
-{
-    TimestampTz min_ts = 0;
-    TimestampTz ref_ts = 0;
-    Oid            inquiry_db;
-    int            count;
-
-    /* already read it? */
-    if (pgStatDBHash)
-        return;
-    Assert(!pgStatRunningInCollector);
-
-    /*
-     * In a normal backend, we check staleness of the data for our own DB, and
-     * so we send MyDatabaseId in inquiry messages.  In the autovac launcher,
-     * check staleness of the shared-catalog data, and send InvalidOid in
-     * inquiry messages so as not to force writing unnecessary data.
-     */
-    if (IsAutoVacuumLauncherProcess())
-        inquiry_db = InvalidOid;
-    else
-        inquiry_db = MyDatabaseId;
-
-    /*
-     * Loop until fresh enough stats file is available or we ran out of time.
-     * The stats inquiry message is sent repeatedly in case collector drops
-     * it; but not every single time, as that just swamps the collector.
-     */
-    for (count = 0; count < PGSTAT_POLL_LOOP_COUNT; count++)
-    {
-        bool        ok;
-        TimestampTz file_ts = 0;
-        TimestampTz cur_ts;
-
-        CHECK_FOR_INTERRUPTS();
-
-        ok = pgstat_read_db_statsfile_timestamp(inquiry_db, false, &file_ts);
-
-        cur_ts = GetCurrentTimestamp();
-        /* Calculate min acceptable timestamp, if we didn't already */
-        if (count == 0 || cur_ts < ref_ts)
-        {
-            /*
-             * We set the minimum acceptable timestamp to PGSTAT_STAT_INTERVAL
-             * msec before now.  This indirectly ensures that the collector
-             * needn't write the file more often than PGSTAT_STAT_INTERVAL. In
-             * an autovacuum worker, however, we want a lower delay to avoid
-             * using stale data, so we use PGSTAT_RETRY_DELAY (since the
-             * number of workers is low, this shouldn't be a problem).
-             *
-             * We don't recompute min_ts after sleeping, except in the
-             * unlikely case that cur_ts went backwards.  So we might end up
-             * accepting a file a bit older than PGSTAT_STAT_INTERVAL.  In
-             * practice that shouldn't happen, though, as long as the sleep
-             * time is less than PGSTAT_STAT_INTERVAL; and we don't want to
-             * tell the collector that our cutoff time is less than what we'd
-             * actually accept.
-             */
-            ref_ts = cur_ts;
-            if (IsAutoVacuumWorkerProcess())
-                min_ts = TimestampTzPlusMilliseconds(ref_ts,
-                                                     -PGSTAT_RETRY_DELAY);
-            else
-                min_ts = TimestampTzPlusMilliseconds(ref_ts,
-                                                     -PGSTAT_STAT_INTERVAL);
-        }
-
-        /*
-         * If the file timestamp is actually newer than cur_ts, we must have
-         * had a clock glitch (system time went backwards) or there is clock
-         * skew between our processor and the stats collector's processor.
-         * Accept the file, but send an inquiry message anyway to make
-         * pgstat_recv_inquiry do a sanity check on the collector's time.
-         */
-        if (ok && file_ts > cur_ts)
-        {
-            /*
-             * A small amount of clock skew between processors isn't terribly
-             * surprising, but a large difference is worth logging.  We
-             * arbitrarily define "large" as 1000 msec.
-             */
-            if (file_ts >= TimestampTzPlusMilliseconds(cur_ts, 1000))
-            {
-                char       *filetime;
-                char       *mytime;
-
-                /* Copy because timestamptz_to_str returns a static buffer */
-                filetime = pstrdup(timestamptz_to_str(file_ts));
-                mytime = pstrdup(timestamptz_to_str(cur_ts));
-                elog(LOG, "stats collector's time %s is later than backend local time %s",
-                     filetime, mytime);
-                pfree(filetime);
-                pfree(mytime);
-            }
-
-            pgstat_send_inquiry(cur_ts, min_ts, inquiry_db);
-            break;
-        }
-
-        /* Normal acceptance case: file is not older than cutoff time */
-        if (ok && file_ts >= min_ts)
-            break;
-
-        /* Not there or too old, so kick the collector and wait a bit */
-        if ((count % PGSTAT_INQ_LOOP_COUNT) == 0)
-            pgstat_send_inquiry(cur_ts, min_ts, inquiry_db);
-
-        pg_usleep(PGSTAT_RETRY_DELAY * 1000L);
-    }
-
-    if (count >= PGSTAT_POLL_LOOP_COUNT)
-        ereport(LOG,
-                (errmsg("using stale statistics instead of current ones "
-                        "because stats collector is not responding")));
-
-    /*
-     * Autovacuum launcher wants stats about all databases, but a shallow read
-     * is sufficient.  Regular backends want a deep read for just the tables
-     * they can see (MyDatabaseId + shared catalogs).
-     */
-    if (IsAutoVacuumLauncherProcess())
-        pgStatDBHash = pgstat_read_statsfiles(InvalidOid, false, false);
-    else
-        pgStatDBHash = pgstat_read_statsfiles(MyDatabaseId, false, true);
-}
-
-
-/* ----------
- * pgstat_setup_memcxt() -
- *
- *    Create pgStatLocalContext, if not already done.
- * ----------
- */
-static void
-pgstat_setup_memcxt(void)
-{
-    if (!pgStatLocalContext)
-        pgStatLocalContext = AllocSetContextCreate(TopMemoryContext,
-                                                   "Statistics snapshot",
-                                                   ALLOCSET_SMALL_SIZES);
-}
-
-
-/* ----------
- * pgstat_clear_snapshot() -
- *
- *    Discard any data collected in the current transaction.  Any subsequent
- *    request will cause new snapshots to be read.
- *
- *    This is also invoked during transaction commit or abort to discard
- *    the no-longer-wanted snapshot.
- * ----------
- */
-void
-pgstat_clear_snapshot(void)
-{
-    /* Release memory, if any was allocated */
-    if (pgStatLocalContext)
-        MemoryContextDelete(pgStatLocalContext);
-
-    /* Reset variables */
-    pgStatLocalContext = NULL;
-    pgStatDBHash = NULL;
-    localBackendStatusTable = NULL;
-    localNumBackends = 0;
-}
-
-
-/* ----------
- * pgstat_recv_inquiry() -
- *
- *    Process stat inquiry requests.
- * ----------
- */
-static void
-pgstat_recv_inquiry(PgStat_MsgInquiry *msg, int len)
-{
-    PgStat_StatDBEntry *dbentry;
-
-    elog(DEBUG2, "received inquiry for database %u", msg->databaseid);
-
-    /*
-     * If there's already a write request for this DB, there's nothing to do.
-     *
-     * Note that if a request is found, we return early and skip the below
-     * check for clock skew.  This is okay, since the only way for a DB
-     * request to be present in the list is that we have been here since the
-     * last write round.  It seems sufficient to check for clock skew once per
-     * write round.
-     */
-    if (list_member_oid(pending_write_requests, msg->databaseid))
-        return;
-
-    /*
-     * Check to see if we last wrote this database at a time >= the requested
-     * cutoff time.  If so, this is a stale request that was generated before
-     * we updated the DB file, and we don't need to do so again.
-     *
-     * If the requestor's local clock time is older than stats_timestamp, we
-     * should suspect a clock glitch, ie system time going backwards; though
-     * the more likely explanation is just delayed message receipt.  It is
-     * worth expending a GetCurrentTimestamp call to be sure, since a large
-     * retreat in the system clock reading could otherwise cause us to neglect
-     * to update the stats file for a long time.
-     */
-    dbentry = pgstat_get_db_entry(msg->databaseid, false);
-    if (dbentry == NULL)
-    {
-        /*
-         * We have no data for this DB.  Enter a write request anyway so that
-         * the global stats will get updated.  This is needed to prevent
-         * backend_read_statsfile from waiting for data that we cannot supply,
-         * in the case of a new DB that nobody has yet reported any stats for.
-         * See the behavior of pgstat_read_db_statsfile_timestamp.
-         */
-    }
-    else if (msg->clock_time < dbentry->stats_timestamp)
-    {
-        TimestampTz cur_ts = GetCurrentTimestamp();
-
-        if (cur_ts < dbentry->stats_timestamp)
-        {
-            /*
-             * Sure enough, time went backwards.  Force a new stats file write
-             * to get back in sync; but first, log a complaint.
-             */
-            char       *writetime;
-            char       *mytime;
-
-            /* Copy because timestamptz_to_str returns a static buffer */
-            writetime = pstrdup(timestamptz_to_str(dbentry->stats_timestamp));
-            mytime = pstrdup(timestamptz_to_str(cur_ts));
-            elog(LOG,
-                 "stats_timestamp %s is later than collector's time %s for database %u",
-                 writetime, mytime, dbentry->databaseid);
-            pfree(writetime);
-            pfree(mytime);
-        }
-        else
-        {
-            /*
-             * Nope, it's just an old request.  Assuming msg's clock_time is
-             * >= its cutoff_time, it must be stale, so we can ignore it.
-             */
-            return;
-        }
-    }
-    else if (msg->cutoff_time <= dbentry->stats_timestamp)
-    {
-        /* Stale request, ignore it */
-        return;
-    }
-
-    /*
-     * We need to write this DB, so create a request.
-     */
-    pending_write_requests = lappend_oid(pending_write_requests,
-                                         msg->databaseid);
-}
-
-
-/* ----------
- * pgstat_recv_tabstat() -
- *
- *    Count what the backend has done.
- * ----------
- */
-static void
-pgstat_recv_tabstat(PgStat_MsgTabstat *msg, int len)
-{
-    PgStat_StatDBEntry *dbentry;
-    PgStat_StatTabEntry *tabentry;
-    int            i;
-    bool        found;
-
-    dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-    /*
-     * Update database-wide stats.
-     */
-    dbentry->n_xact_commit += (PgStat_Counter) (msg->m_xact_commit);
-    dbentry->n_xact_rollback += (PgStat_Counter) (msg->m_xact_rollback);
-    dbentry->n_block_read_time += msg->m_block_read_time;
-    dbentry->n_block_write_time += msg->m_block_write_time;
-
-    /*
-     * Process all table entries in the message.
-     */
-    for (i = 0; i < msg->m_nentries; i++)
-    {
-        PgStat_TableEntry *tabmsg = &(msg->m_entry[i]);
-
-        tabentry = (PgStat_StatTabEntry *) hash_search(dbentry->tables,
-                                                       (void *) &(tabmsg->t_id),
-                                                       HASH_ENTER, &found);
-
-        if (!found)
-        {
-            /*
-             * If it's a new table entry, initialize counters to the values we
-             * just got.
-             */
-            tabentry->numscans = tabmsg->t_counts.t_numscans;
-            tabentry->tuples_returned = tabmsg->t_counts.t_tuples_returned;
-            tabentry->tuples_fetched = tabmsg->t_counts.t_tuples_fetched;
-            tabentry->tuples_inserted = tabmsg->t_counts.t_tuples_inserted;
-            tabentry->tuples_updated = tabmsg->t_counts.t_tuples_updated;
-            tabentry->tuples_deleted = tabmsg->t_counts.t_tuples_deleted;
-            tabentry->tuples_hot_updated = tabmsg->t_counts.t_tuples_hot_updated;
-            tabentry->n_live_tuples = tabmsg->t_counts.t_delta_live_tuples;
-            tabentry->n_dead_tuples = tabmsg->t_counts.t_delta_dead_tuples;
-            tabentry->changes_since_analyze = tabmsg->t_counts.t_changed_tuples;
-            tabentry->blocks_fetched = tabmsg->t_counts.t_blocks_fetched;
-            tabentry->blocks_hit = tabmsg->t_counts.t_blocks_hit;
-
-            tabentry->vacuum_timestamp = 0;
-            tabentry->vacuum_count = 0;
-            tabentry->autovac_vacuum_timestamp = 0;
-            tabentry->autovac_vacuum_count = 0;
-            tabentry->analyze_timestamp = 0;
-            tabentry->analyze_count = 0;
-            tabentry->autovac_analyze_timestamp = 0;
-            tabentry->autovac_analyze_count = 0;
-        }
-        else
-        {
-            /*
-             * Otherwise add the values to the existing entry.
-             */
-            tabentry->numscans += tabmsg->t_counts.t_numscans;
-            tabentry->tuples_returned += tabmsg->t_counts.t_tuples_returned;
-            tabentry->tuples_fetched += tabmsg->t_counts.t_tuples_fetched;
-            tabentry->tuples_inserted += tabmsg->t_counts.t_tuples_inserted;
-            tabentry->tuples_updated += tabmsg->t_counts.t_tuples_updated;
-            tabentry->tuples_deleted += tabmsg->t_counts.t_tuples_deleted;
-            tabentry->tuples_hot_updated += tabmsg->t_counts.t_tuples_hot_updated;
-            /* If table was truncated, first reset the live/dead counters */
-            if (tabmsg->t_counts.t_truncated)
-            {
-                tabentry->n_live_tuples = 0;
-                tabentry->n_dead_tuples = 0;
-            }
-            tabentry->n_live_tuples += tabmsg->t_counts.t_delta_live_tuples;
-            tabentry->n_dead_tuples += tabmsg->t_counts.t_delta_dead_tuples;
-            tabentry->changes_since_analyze += tabmsg->t_counts.t_changed_tuples;
-            tabentry->blocks_fetched += tabmsg->t_counts.t_blocks_fetched;
-            tabentry->blocks_hit += tabmsg->t_counts.t_blocks_hit;
-        }
-
-        /* Clamp n_live_tuples in case of negative delta_live_tuples */
-        tabentry->n_live_tuples = Max(tabentry->n_live_tuples, 0);
-        /* Likewise for n_dead_tuples */
-        tabentry->n_dead_tuples = Max(tabentry->n_dead_tuples, 0);
-
-        /*
-         * Add per-table stats to the per-database entry, too.
-         */
-        dbentry->n_tuples_returned += tabmsg->t_counts.t_tuples_returned;
-        dbentry->n_tuples_fetched += tabmsg->t_counts.t_tuples_fetched;
-        dbentry->n_tuples_inserted += tabmsg->t_counts.t_tuples_inserted;
-        dbentry->n_tuples_updated += tabmsg->t_counts.t_tuples_updated;
-        dbentry->n_tuples_deleted += tabmsg->t_counts.t_tuples_deleted;
-        dbentry->n_blocks_fetched += tabmsg->t_counts.t_blocks_fetched;
-        dbentry->n_blocks_hit += tabmsg->t_counts.t_blocks_hit;
-    }
-}
-
-
-/* ----------
- * pgstat_recv_tabpurge() -
- *
- *    Arrange for dead table removal.
- * ----------
- */
-static void
-pgstat_recv_tabpurge(PgStat_MsgTabpurge *msg, int len)
-{
-    PgStat_StatDBEntry *dbentry;
-    int            i;
-
-    dbentry = pgstat_get_db_entry(msg->m_databaseid, false);
-
-    /*
-     * No need to purge if we don't even know the database.
-     */
-    if (!dbentry || !dbentry->tables)
-        return;
-
-    /*
-     * Process all table entries in the message.
-     */
-    for (i = 0; i < msg->m_nentries; i++)
-    {
-        /* Remove from hashtable if present; we don't care if it's not. */
-        (void) hash_search(dbentry->tables,
-                           (void *) &(msg->m_tableid[i]),
-                           HASH_REMOVE, NULL);
-    }
-}
-
-
-/* ----------
- * pgstat_recv_dropdb() -
- *
- *    Arrange for dead database removal
- * ----------
- */
-static void
-pgstat_recv_dropdb(PgStat_MsgDropdb *msg, int len)
-{
-    Oid            dbid = msg->m_databaseid;
-    PgStat_StatDBEntry *dbentry;
-
-    /*
-     * Lookup the database in the hashtable.
-     */
-    dbentry = pgstat_get_db_entry(dbid, false);
-
-    /*
-     * If found, remove it (along with the db statfile).
-     */
-    if (dbentry)
-    {
-        char        statfile[MAXPGPATH];
-
-        get_dbstat_filename(false, false, dbid, statfile, MAXPGPATH);
-
-        elog(DEBUG2, "removing stats file \"%s\"", statfile);
-        unlink(statfile);
-
-        if (dbentry->tables != NULL)
-            hash_destroy(dbentry->tables);
-        if (dbentry->functions != NULL)
-            hash_destroy(dbentry->functions);
-
-        if (hash_search(pgStatDBHash,
-                        (void *) &dbid,
-                        HASH_REMOVE, NULL) == NULL)
-            ereport(ERROR,
-                    (errmsg("database hash table corrupted during cleanup --- abort")));
-    }
-}
-
-
-/* ----------
- * pgstat_recv_resetcounter() -
- *
- *    Reset the statistics for the specified database.
- * ----------
- */
-static void
-pgstat_recv_resetcounter(PgStat_MsgResetcounter *msg, int len)
-{
-    PgStat_StatDBEntry *dbentry;
-
-    /*
-     * Lookup the database in the hashtable.  Nothing to do if not there.
-     */
-    dbentry = pgstat_get_db_entry(msg->m_databaseid, false);
-
-    if (!dbentry)
-        return;
-
-    /*
-     * We simply throw away all the database's table entries by recreating a
-     * new hash table for them.
-     */
-    if (dbentry->tables != NULL)
-        hash_destroy(dbentry->tables);
-    if (dbentry->functions != NULL)
-        hash_destroy(dbentry->functions);
-
-    dbentry->tables = NULL;
-    dbentry->functions = NULL;
-
-    /*
-     * Reset database-level stats, too.  This creates empty hash tables for
-     * tables and functions.
-     */
-    reset_dbentry_counters(dbentry);
-}
-
-/* ----------
- * pgstat_recv_resetshared() -
- *
- *    Reset some shared statistics of the cluster.
- * ----------
- */
-static void
-pgstat_recv_resetsharedcounter(PgStat_MsgResetsharedcounter *msg, int len)
-{
-    if (msg->m_resettarget == RESET_BGWRITER)
-    {
-        /* Reset the global background writer statistics for the cluster. */
-        memset(&globalStats, 0, sizeof(globalStats));
-        globalStats.stat_reset_timestamp = GetCurrentTimestamp();
-    }
-    else if (msg->m_resettarget == RESET_ARCHIVER)
-    {
-        /* Reset the archiver statistics for the cluster. */
-        memset(&archiverStats, 0, sizeof(archiverStats));
-        archiverStats.stat_reset_timestamp = GetCurrentTimestamp();
-    }
-
-    /*
-     * Presumably the sender of this message validated the target, don't
-     * complain here if it's not valid
-     */
-}
-
-/* ----------
- * pgstat_recv_resetsinglecounter() -
- *
- *    Reset a statistics for a single object
- * ----------
- */
-static void
-pgstat_recv_resetsinglecounter(PgStat_MsgResetsinglecounter *msg, int len)
-{
-    PgStat_StatDBEntry *dbentry;
-
-    dbentry = pgstat_get_db_entry(msg->m_databaseid, false);
-
-    if (!dbentry)
-        return;
-
-    /* Set the reset timestamp for the whole database */
-    dbentry->stat_reset_timestamp = GetCurrentTimestamp();
-
-    /* Remove object if it exists, ignore it if not */
-    if (msg->m_resettype == RESET_TABLE)
-        (void) hash_search(dbentry->tables, (void *) &(msg->m_objectid),
-                           HASH_REMOVE, NULL);
-    else if (msg->m_resettype == RESET_FUNCTION)
-        (void) hash_search(dbentry->functions, (void *) &(msg->m_objectid),
-                           HASH_REMOVE, NULL);
-}
-
-/* ----------
- * pgstat_recv_autovac() -
- *
- *    Process an autovacuum signalling message.
- * ----------
- */
-static void
-pgstat_recv_autovac(PgStat_MsgAutovacStart *msg, int len)
-{
-    PgStat_StatDBEntry *dbentry;
-
-    /*
-     * Store the last autovacuum time in the database's hashtable entry.
-     */
-    dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-    dbentry->last_autovac_time = msg->m_start_time;
-}
-
-/* ----------
- * pgstat_recv_vacuum() -
- *
- *    Process a VACUUM message.
- * ----------
- */
-static void
-pgstat_recv_vacuum(PgStat_MsgVacuum *msg, int len)
-{
-    PgStat_StatDBEntry *dbentry;
-    PgStat_StatTabEntry *tabentry;
-
-    /*
-     * Store the data in the table's hashtable entry.
-     */
-    dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-    tabentry = pgstat_get_tab_entry(dbentry, msg->m_tableoid, true);
-
-    tabentry->n_live_tuples = msg->m_live_tuples;
-    tabentry->n_dead_tuples = msg->m_dead_tuples;
-
-    if (msg->m_autovacuum)
-    {
-        tabentry->autovac_vacuum_timestamp = msg->m_vacuumtime;
-        tabentry->autovac_vacuum_count++;
-    }
-    else
-    {
-        tabentry->vacuum_timestamp = msg->m_vacuumtime;
-        tabentry->vacuum_count++;
-    }
-}
-
-/* ----------
- * pgstat_recv_analyze() -
- *
- *    Process an ANALYZE message.
- * ----------
- */
-static void
-pgstat_recv_analyze(PgStat_MsgAnalyze *msg, int len)
-{
-    PgStat_StatDBEntry *dbentry;
-    PgStat_StatTabEntry *tabentry;
-
-    /*
-     * Store the data in the table's hashtable entry.
-     */
-    dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-    tabentry = pgstat_get_tab_entry(dbentry, msg->m_tableoid, true);
-
-    tabentry->n_live_tuples = msg->m_live_tuples;
-    tabentry->n_dead_tuples = msg->m_dead_tuples;
-
-    /*
-     * If commanded, reset changes_since_analyze to zero.  This forgets any
-     * changes that were committed while the ANALYZE was in progress, but we
-     * have no good way to estimate how many of those there were.
-     */
-    if (msg->m_resetcounter)
-        tabentry->changes_since_analyze = 0;
-
-    if (msg->m_autovacuum)
-    {
-        tabentry->autovac_analyze_timestamp = msg->m_analyzetime;
-        tabentry->autovac_analyze_count++;
-    }
-    else
-    {
-        tabentry->analyze_timestamp = msg->m_analyzetime;
-        tabentry->analyze_count++;
-    }
-}
-
-
-/* ----------
- * pgstat_recv_archiver() -
- *
- *    Process a ARCHIVER message.
- * ----------
- */
-static void
-pgstat_recv_archiver(PgStat_MsgArchiver *msg, int len)
-{
-    if (msg->m_failed)
-    {
-        /* Failed archival attempt */
-        ++archiverStats.failed_count;
-        memcpy(archiverStats.last_failed_wal, msg->m_xlog,
-               sizeof(archiverStats.last_failed_wal));
-        archiverStats.last_failed_timestamp = msg->m_timestamp;
-    }
-    else
-    {
-        /* Successful archival operation */
-        ++archiverStats.archived_count;
-        memcpy(archiverStats.last_archived_wal, msg->m_xlog,
-               sizeof(archiverStats.last_archived_wal));
-        archiverStats.last_archived_timestamp = msg->m_timestamp;
-    }
-}
-
-/* ----------
- * pgstat_recv_bgwriter() -
- *
- *    Process a BGWRITER message.
- * ----------
- */
-static void
-pgstat_recv_bgwriter(PgStat_MsgBgWriter *msg, int len)
-{
-    globalStats.timed_checkpoints += msg->m_timed_checkpoints;
-    globalStats.requested_checkpoints += msg->m_requested_checkpoints;
-    globalStats.checkpoint_write_time += msg->m_checkpoint_write_time;
-    globalStats.checkpoint_sync_time += msg->m_checkpoint_sync_time;
-    globalStats.buf_written_checkpoints += msg->m_buf_written_checkpoints;
-    globalStats.buf_written_clean += msg->m_buf_written_clean;
-    globalStats.maxwritten_clean += msg->m_maxwritten_clean;
-    globalStats.buf_written_backend += msg->m_buf_written_backend;
-    globalStats.buf_fsync_backend += msg->m_buf_fsync_backend;
-    globalStats.buf_alloc += msg->m_buf_alloc;
-}
-
-/* ----------
- * pgstat_recv_recoveryconflict() -
- *
- *    Process a RECOVERYCONFLICT message.
- * ----------
- */
-static void
-pgstat_recv_recoveryconflict(PgStat_MsgRecoveryConflict *msg, int len)
-{
-    PgStat_StatDBEntry *dbentry;
-
-    dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-    switch (msg->m_reason)
-    {
-        case PROCSIG_RECOVERY_CONFLICT_DATABASE:
-
-            /*
-             * Since we drop the information about the database as soon as it
-             * replicates, there is no point in counting these conflicts.
-             */
-            break;
-        case PROCSIG_RECOVERY_CONFLICT_TABLESPACE:
-            dbentry->n_conflict_tablespace++;
-            break;
-        case PROCSIG_RECOVERY_CONFLICT_LOCK:
-            dbentry->n_conflict_lock++;
-            break;
-        case PROCSIG_RECOVERY_CONFLICT_SNAPSHOT:
-            dbentry->n_conflict_snapshot++;
-            break;
-        case PROCSIG_RECOVERY_CONFLICT_BUFFERPIN:
-            dbentry->n_conflict_bufferpin++;
-            break;
-        case PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK:
-            dbentry->n_conflict_startup_deadlock++;
-            break;
-    }
-}
-
-/* ----------
- * pgstat_recv_deadlock() -
- *
- *    Process a DEADLOCK message.
- * ----------
- */
-static void
-pgstat_recv_deadlock(PgStat_MsgDeadlock *msg, int len)
-{
-    PgStat_StatDBEntry *dbentry;
-
-    dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-    dbentry->n_deadlocks++;
-}
-
-/* ----------
- * pgstat_recv_tempfile() -
- *
- *    Process a TEMPFILE message.
- * ----------
- */
-static void
-pgstat_recv_tempfile(PgStat_MsgTempFile *msg, int len)
-{
-    PgStat_StatDBEntry *dbentry;
-
-    dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-    dbentry->n_temp_bytes += msg->m_filesize;
-    dbentry->n_temp_files += 1;
-}
-
-/* ----------
- * pgstat_recv_funcstat() -
- *
- *    Count what the backend has done.
- * ----------
- */
-static void
-pgstat_recv_funcstat(PgStat_MsgFuncstat *msg, int len)
-{
-    PgStat_FunctionEntry *funcmsg = &(msg->m_entry[0]);
-    PgStat_StatDBEntry *dbentry;
-    PgStat_StatFuncEntry *funcentry;
-    int            i;
-    bool        found;
-
-    dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-    /*
-     * Process all function entries in the message.
-     */
-    for (i = 0; i < msg->m_nentries; i++, funcmsg++)
-    {
-        funcentry = (PgStat_StatFuncEntry *) hash_search(dbentry->functions,
-                                                         (void *) &(funcmsg->f_id),
-                                                         HASH_ENTER, &found);
-
-        if (!found)
-        {
-            /*
-             * If it's a new function entry, initialize counters to the values
-             * we just got.
-             */
-            funcentry->f_numcalls = funcmsg->f_numcalls;
-            funcentry->f_total_time = funcmsg->f_total_time;
-            funcentry->f_self_time = funcmsg->f_self_time;
-        }
-        else
-        {
-            /*
-             * Otherwise add the values to the existing entry.
-             */
-            funcentry->f_numcalls += funcmsg->f_numcalls;
-            funcentry->f_total_time += funcmsg->f_total_time;
-            funcentry->f_self_time += funcmsg->f_self_time;
-        }
-    }
-}
-
-/* ----------
- * pgstat_recv_funcpurge() -
- *
- *    Arrange for dead function removal.
- * ----------
- */
-static void
-pgstat_recv_funcpurge(PgStat_MsgFuncpurge *msg, int len)
-{
-    PgStat_StatDBEntry *dbentry;
-    int            i;
-
-    dbentry = pgstat_get_db_entry(msg->m_databaseid, false);
-
-    /*
-     * No need to purge if we don't even know the database.
-     */
-    if (!dbentry || !dbentry->functions)
-        return;
-
-    /*
-     * Process all function entries in the message.
-     */
-    for (i = 0; i < msg->m_nentries; i++)
-    {
-        /* Remove from hashtable if present; we don't care if it's not. */
-        (void) hash_search(dbentry->functions,
-                           (void *) &(msg->m_functionid[i]),
-                           HASH_REMOVE, NULL);
-    }
-}
-
-/* ----------
- * pgstat_write_statsfile_needed() -
- *
- *    Do we need to write out any stats files?
- * ----------
- */
-static bool
-pgstat_write_statsfile_needed(void)
-{
-    if (pending_write_requests != NIL)
-        return true;
-
-    /* Everything was written recently */
-    return false;
-}
-
-/* ----------
- * pgstat_db_requested() -
- *
- *    Checks whether stats for a particular DB need to be written to a file.
- * ----------
- */
-static bool
-pgstat_db_requested(Oid databaseid)
-{
-    /*
-     * If any requests are outstanding at all, we should write the stats for
-     * shared catalogs (the "database" with OID 0).  This ensures that
-     * backends will see up-to-date stats for shared catalogs, even though
-     * they send inquiry messages mentioning only their own DB.
-     */
-    if (databaseid == InvalidOid && pending_write_requests != NIL)
-        return true;
-
-    /* Search to see if there's an open request to write this database. */
-    if (list_member_oid(pending_write_requests, databaseid))
-        return true;
-
-    return false;
-}
-
 /*
  * Convert a potentially unsafely truncated activity string (see
  * PgBackendStatus.st_activity_raw's documentation) into a correctly truncated
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 820f356038..369d6dde63 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -255,7 +255,6 @@ static pid_t StartupPID = 0,
             WalReceiverPID = 0,
             AutoVacPID = 0,
             PgArchPID = 0,
-            PgStatPID = 0,
             SysLoggerPID = 0;
 
 /* Startup process's status */
@@ -502,7 +501,6 @@ typedef struct
     PGPROC       *AuxiliaryProcs;
     PGPROC       *PreparedXactProcs;
     PMSignalData *PMSignalState;
-    InheritableSocket pgStatSock;
     pid_t        PostmasterPid;
     TimestampTz PgStartTime;
     TimestampTz PgReloadTime;
@@ -1302,12 +1300,6 @@ PostmasterMain(int argc, char *argv[])
      */
     RemovePgTempFiles();
 
-    /*
-     * Initialize stats collection subsystem (this does NOT start the
-     * collector process!)
-     */
-    pgstat_init();
-
     /*
      * Initialize the autovacuum subsystem (again, no process start yet)
      */
@@ -1756,11 +1748,6 @@ ServerLoop(void)
                 start_autovac_launcher = false; /* signal processed */
         }
 
-        /* If we have lost the stats collector, try to start a new one */
-        if (PgStatPID == 0 &&
-            (pmState == PM_RUN || pmState == PM_HOT_STANDBY))
-            PgStatPID = pgstat_start();
-
         /* If we have lost the archiver, try to start a new one. */
         if (PgArchPID == 0 && PgArchStartupAllowed())
             PgArchPID = StartArchiver();
@@ -2595,8 +2582,6 @@ SIGHUP_handler(SIGNAL_ARGS)
             signal_child(PgArchPID, SIGHUP);
         if (SysLoggerPID != 0)
             signal_child(SysLoggerPID, SIGHUP);
-        if (PgStatPID != 0)
-            signal_child(PgStatPID, SIGHUP);
 
         /* Reload authentication config files too */
         if (!load_hba())
@@ -2927,8 +2912,6 @@ reaper(SIGNAL_ARGS)
                 AutoVacPID = StartAutoVacLauncher();
             if (PgArchStartupAllowed() && PgArchPID == 0)
                 PgArchPID = StartArchiver();
-            if (PgStatPID == 0)
-                PgStatPID = pgstat_start();
 
             /* workers may be scheduled to start now */
             maybe_start_bgworkers();
@@ -2995,13 +2978,6 @@ reaper(SIGNAL_ARGS)
                 SignalChildren(SIGUSR2);
 
                 pmState = PM_SHUTDOWN_2;
-
-                /*
-                 * We can also shut down the stats collector now; there's
-                 * nothing left for it to do.
-                 */
-                if (PgStatPID != 0)
-                    signal_child(PgStatPID, SIGQUIT);
             }
             else
             {
@@ -3076,22 +3052,6 @@ reaper(SIGNAL_ARGS)
             continue;
         }
 
-        /*
-         * Was it the statistics collector?  If so, just try to start a new
-         * one; no need to force reset of the rest of the system.  (If fail,
-         * we'll try again in future cycles of the main loop.)
-         */
-        if (pid == PgStatPID)
-        {
-            PgStatPID = 0;
-            if (!EXIT_STATUS_0(exitstatus))
-                LogChildExit(LOG, _("statistics collector process"),
-                             pid, exitstatus);
-            if (pmState == PM_RUN || pmState == PM_HOT_STANDBY)
-                PgStatPID = pgstat_start();
-            continue;
-        }
-
         /* Was it the system logger?  If so, try to start a new one */
         if (pid == SysLoggerPID)
         {
@@ -3550,22 +3510,6 @@ HandleChildCrash(int pid, int exitstatus, const char *procname)
         signal_child(PgArchPID, SIGQUIT);
     }
 
-    /*
-     * Force a power-cycle of the pgstat process too.  (This isn't absolutely
-     * necessary, but it seems like a good idea for robustness, and it
-     * simplifies the state-machine logic in the case where a shutdown request
-     * arrives during crash processing.)
-     */
-    if (PgStatPID != 0 && take_action)
-    {
-        ereport(DEBUG2,
-                (errmsg_internal("sending %s to process %d",
-                                 "SIGQUIT",
-                                 (int) PgStatPID)));
-        signal_child(PgStatPID, SIGQUIT);
-        allow_immediate_pgstat_restart();
-    }
-
     /* We do NOT restart the syslogger */
 
     if (Shutdown != ImmediateShutdown)
@@ -3761,8 +3705,6 @@ PostmasterStateMachine(void)
                     SignalChildren(SIGQUIT);
                     if (PgArchPID != 0)
                         signal_child(PgArchPID, SIGQUIT);
-                    if (PgStatPID != 0)
-                        signal_child(PgStatPID, SIGQUIT);
                 }
             }
         }
@@ -3801,8 +3743,7 @@ PostmasterStateMachine(void)
          * normal state transition leading up to PM_WAIT_DEAD_END, or during
          * FatalError processing.
          */
-        if (dlist_is_empty(&BackendList) &&
-            PgArchPID == 0 && PgStatPID == 0)
+        if (dlist_is_empty(&BackendList) && PgArchPID == 0)
         {
             /* These other guys should be dead already */
             Assert(StartupPID == 0);
@@ -4003,8 +3944,6 @@ TerminateChildren(int signal)
         signal_child(AutoVacPID, signal);
     if (PgArchPID != 0)
         signal_child(PgArchPID, signal);
-    if (PgStatPID != 0)
-        signal_child(PgStatPID, signal);
 }
 
 /*
@@ -4977,18 +4916,6 @@ SubPostmasterMain(int argc, char *argv[])
 
         StartBackgroundWorker();
     }
-    if (strcmp(argv[1], "--forkarch") == 0)
-    {
-        /* Do not want to attach to shared memory */
-
-        PgArchiverMain(argc, argv); /* does not return */
-    }
-    if (strcmp(argv[1], "--forkcol") == 0)
-    {
-        /* Do not want to attach to shared memory */
-
-        PgstatCollectorMain(argc, argv);    /* does not return */
-    }
     if (strcmp(argv[1], "--forklog") == 0)
     {
         /* Do not want to attach to shared memory */
@@ -5101,12 +5028,6 @@ sigusr1_handler(SIGNAL_ARGS)
     if (CheckPostmasterSignal(PMSIGNAL_BEGIN_HOT_STANDBY) &&
         pmState == PM_RECOVERY && Shutdown == NoShutdown)
     {
-        /*
-         * Likewise, start other special children as needed.
-         */
-        Assert(PgStatPID == 0);
-        PgStatPID = pgstat_start();
-
         ereport(LOG,
                 (errmsg("database system is ready to accept read only connections")));
 
@@ -5976,7 +5897,6 @@ extern slock_t *ShmemLock;
 extern slock_t *ProcStructLock;
 extern PGPROC *AuxiliaryProcs;
 extern PMSignalData *PMSignalState;
-extern pgsocket pgStatSock;
 extern pg_time_t first_syslogger_file_time;
 
 #ifndef WIN32
@@ -6029,8 +5949,6 @@ save_backend_variables(BackendParameters *param, Port *port,
     param->AuxiliaryProcs = AuxiliaryProcs;
     param->PreparedXactProcs = PreparedXactProcs;
     param->PMSignalState = PMSignalState;
-    if (!write_inheritable_socket(¶m->pgStatSock, pgStatSock, childPid))
-        return false;
 
     param->PostmasterPid = PostmasterPid;
     param->PgStartTime = PgStartTime;
@@ -6262,7 +6180,6 @@ restore_backend_variables(BackendParameters *param, Port *port)
     AuxiliaryProcs = param->AuxiliaryProcs;
     PreparedXactProcs = param->PreparedXactProcs;
     PMSignalState = param->PMSignalState;
-    read_inheritable_socket(&pgStatSock, ¶m->pgStatSock);
 
     PostmasterPid = param->PostmasterPid;
     PgStartTime = param->PgStartTime;
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 5965d3620f..97bca9be24 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -150,6 +150,7 @@ CreateSharedMemoryAndSemaphores(bool makePrivate, int port)
         size = add_size(size, BTreeShmemSize());
         size = add_size(size, SyncScanShmemSize());
         size = add_size(size, AsyncShmemSize());
+        size = add_size(size, StatsShmemSize());
 #ifdef EXEC_BACKEND
         size = add_size(size, ShmemBackendArraySize());
 #endif
@@ -281,8 +282,13 @@ CreateSharedMemoryAndSemaphores(bool makePrivate, int port)
 
     /* Initialize dynamic shared memory facilities. */
     if (!IsUnderPostmaster)
+    {
         dsm_postmaster_startup(shim);
 
+        /* Stats collector uses dynamic shared memory  */
+        StatsShmemInit();
+    }
+
     /*
      * Now give loadable modules a chance to set up their shmem allocations
      */
diff --git a/src/backend/storage/lmgr/lwlock.c b/src/backend/storage/lmgr/lwlock.c
index 81dac45ae5..004cb26f63 100644
--- a/src/backend/storage/lmgr/lwlock.c
+++ b/src/backend/storage/lmgr/lwlock.c
@@ -521,6 +521,7 @@ RegisterLWLockTranches(void)
     LWLockRegisterTranche(LWTRANCHE_TBM, "tbm");
     LWLockRegisterTranche(LWTRANCHE_PARALLEL_APPEND, "parallel_append");
     LWLockRegisterTranche(LWTRANCHE_PARALLEL_HASH_JOIN, "parallel_hash_join");
+    LWLockRegisterTranche(LWTRANCHE_STATS, "activity stats");
 
     /* Register named tranches. */
     for (i = 0; i < NamedLWLockTrancheRequests; i++)
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 8b4d94c9a1..fc265a507e 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -3159,6 +3159,12 @@ ProcessInterrupts(void)
 
     if (ParallelMessagePending)
         HandleParallelMessages();
+
+    if (IdleStatsUpdateTimeoutPending)
+    {
+        IdleStatsUpdateTimeoutPending = false;
+        pgstat_report_stat(true);
+    }
 }
 
 
@@ -3733,6 +3739,7 @@ PostgresMain(int argc, char *argv[],
     sigjmp_buf    local_sigjmp_buf;
     volatile bool send_ready_for_query = true;
     bool        disable_idle_in_transaction_timeout = false;
+    bool        disable_idle_stats_update_timeout = false;
 
     /* Initialize startup process environment if necessary. */
     if (!IsUnderPostmaster)
@@ -4173,9 +4180,17 @@ PostgresMain(int argc, char *argv[],
             }
             else
             {
-                ProcessCompletedNotifies();
-                pgstat_report_stat(false);
+                long stats_timeout;
 
+                ProcessCompletedNotifies();
+
+                stats_timeout = pgstat_report_stat(false);
+                if (stats_timeout > 0)
+                {
+                    disable_idle_stats_update_timeout = true;
+                    enable_timeout_after(IDLE_STATS_UPDATE_TIMEOUT,
+                                         stats_timeout);
+                }
                 set_ps_display("idle", false);
                 pgstat_report_activity(STATE_IDLE, NULL);
             }
@@ -4210,7 +4225,7 @@ PostgresMain(int argc, char *argv[],
         DoingCommandRead = false;
 
         /*
-         * (5) turn off the idle-in-transaction timeout
+         * (5) turn off the idle-in-transaction timeout and stats update timeout
          */
         if (disable_idle_in_transaction_timeout)
         {
@@ -4218,6 +4233,12 @@ PostgresMain(int argc, char *argv[],
             disable_idle_in_transaction_timeout = false;
         }
 
+        if (disable_idle_stats_update_timeout)
+        {
+            disable_timeout(IDLE_STATS_UPDATE_TIMEOUT, false);
+            disable_idle_stats_update_timeout = false;
+        }
+
         /*
          * (6) check for any other interesting events that happened while we
          * slept.
diff --git a/src/backend/utils/init/globals.c b/src/backend/utils/init/globals.c
index fd51934aaf..994351ac2d 100644
--- a/src/backend/utils/init/globals.c
+++ b/src/backend/utils/init/globals.c
@@ -32,6 +32,7 @@ volatile sig_atomic_t QueryCancelPending = false;
 volatile sig_atomic_t ProcDiePending = false;
 volatile sig_atomic_t ClientConnectionLost = false;
 volatile sig_atomic_t IdleInTransactionSessionTimeoutPending = false;
+volatile sig_atomic_t IdleStatsUpdateTimeoutPending = false;
 volatile sig_atomic_t ConfigReloadPending = false;
 volatile uint32 InterruptHoldoffCount = 0;
 volatile uint32 QueryCancelHoldoffCount = 0;
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index a5ee209f91..5e67b25e18 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -72,6 +72,7 @@ static void ShutdownPostgres(int code, Datum arg);
 static void StatementTimeoutHandler(void);
 static void LockTimeoutHandler(void);
 static void IdleInTransactionSessionTimeoutHandler(void);
+static void IdleStatsUpdateTimeoutHandler(void);
 static bool ThereIsAtLeastOneRole(void);
 static void process_startup_options(Port *port, bool am_superuser);
 static void process_settings(Oid databaseid, Oid roleid);
@@ -628,6 +629,8 @@ InitPostgres(const char *in_dbname, Oid dboid, const char *username,
         RegisterTimeout(LOCK_TIMEOUT, LockTimeoutHandler);
         RegisterTimeout(IDLE_IN_TRANSACTION_SESSION_TIMEOUT,
                         IdleInTransactionSessionTimeoutHandler);
+        RegisterTimeout(IDLE_STATS_UPDATE_TIMEOUT,
+                        IdleStatsUpdateTimeoutHandler);
     }
 
     /*
@@ -1238,6 +1241,14 @@ IdleInTransactionSessionTimeoutHandler(void)
     SetLatch(MyLatch);
 }
 
+static void
+IdleStatsUpdateTimeoutHandler(void)
+{
+    IdleStatsUpdateTimeoutPending = true;
+    InterruptPending = true;
+    SetLatch(MyLatch);
+}
+
 /*
  * Returns true if at least one role is defined in this database cluster.
  */
diff --git a/src/bin/pg_basebackup/t/010_pg_basebackup.pl b/src/bin/pg_basebackup/t/010_pg_basebackup.pl
index 33869fecc9..8939758c59 100644
--- a/src/bin/pg_basebackup/t/010_pg_basebackup.pl
+++ b/src/bin/pg_basebackup/t/010_pg_basebackup.pl
@@ -123,7 +123,7 @@ is_deeply(
 
 # Contents of these directories should not be copied.
 foreach my $dirname (
-    qw(pg_dynshmem pg_notify pg_replslot pg_serial pg_snapshots pg_stat_tmp pg_subtrans)
+    qw(pg_dynshmem pg_notify pg_replslot pg_serial pg_snapshots pg_subtrans)
   )
 {
     is_deeply(
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 63a7653457..c67331138b 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -82,6 +82,7 @@ extern PGDLLIMPORT volatile sig_atomic_t InterruptPending;
 extern PGDLLIMPORT volatile sig_atomic_t QueryCancelPending;
 extern PGDLLIMPORT volatile sig_atomic_t ProcDiePending;
 extern PGDLLIMPORT volatile sig_atomic_t IdleInTransactionSessionTimeoutPending;
+extern PGDLLIMPORT volatile sig_atomic_t IdleStatsUpdateTimeoutPending;
 extern PGDLLIMPORT volatile sig_atomic_t ConfigReloadPending;
 
 extern PGDLLIMPORT volatile sig_atomic_t ClientConnectionLost;
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index 3324be8a81..cb70d00b8f 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -1,7 +1,7 @@
 /* ----------
  *    pgstat.h
  *
- *    Definitions for the PostgreSQL statistics collector daemon.
+ *    Definitions for the PostgreSQL statistics collector facility.
  *
  *    Copyright (c) 2001-2019, PostgreSQL Global Development Group
  *
@@ -14,10 +14,11 @@
 #include "datatype/timestamp.h"
 #include "fmgr.h"
 #include "libpq/pqcomm.h"
-#include "port/atomics.h"
+#include "lib/dshash.h"
 #include "portability/instr_time.h"
 #include "postmaster/pgarch.h"
 #include "storage/proc.h"
+#include "storage/lwlock.h"
 #include "utils/hsearch.h"
 #include "utils/relcache.h"
 
@@ -41,32 +42,6 @@ typedef enum TrackFunctionsLevel
     TRACK_FUNC_ALL
 }            TrackFunctionsLevel;
 
-/* ----------
- * The types of backend -> collector messages
- * ----------
- */
-typedef enum StatMsgType
-{
-    PGSTAT_MTYPE_DUMMY,
-    PGSTAT_MTYPE_INQUIRY,
-    PGSTAT_MTYPE_TABSTAT,
-    PGSTAT_MTYPE_TABPURGE,
-    PGSTAT_MTYPE_DROPDB,
-    PGSTAT_MTYPE_RESETCOUNTER,
-    PGSTAT_MTYPE_RESETSHAREDCOUNTER,
-    PGSTAT_MTYPE_RESETSINGLECOUNTER,
-    PGSTAT_MTYPE_AUTOVAC_START,
-    PGSTAT_MTYPE_VACUUM,
-    PGSTAT_MTYPE_ANALYZE,
-    PGSTAT_MTYPE_ARCHIVER,
-    PGSTAT_MTYPE_BGWRITER,
-    PGSTAT_MTYPE_FUNCSTAT,
-    PGSTAT_MTYPE_FUNCPURGE,
-    PGSTAT_MTYPE_RECOVERYCONFLICT,
-    PGSTAT_MTYPE_TEMPFILE,
-    PGSTAT_MTYPE_DEADLOCK
-} StatMsgType;
-
 /* ----------
  * The data type used for counters.
  * ----------
@@ -115,13 +90,6 @@ typedef struct PgStat_TableCounts
     PgStat_Counter t_blocks_hit;
 } PgStat_TableCounts;
 
-/* Possible targets for resetting cluster-wide shared values */
-typedef enum PgStat_Shared_Reset_Target
-{
-    RESET_ARCHIVER,
-    RESET_BGWRITER
-} PgStat_Shared_Reset_Target;
-
 /* Possible object types for resetting single counters */
 typedef enum PgStat_Single_Reset_Type
 {
@@ -180,236 +148,12 @@ typedef struct PgStat_TableXactStatus
 } PgStat_TableXactStatus;
 
 
-/* ------------------------------------------------------------
- * Message formats follow
- * ------------------------------------------------------------
- */
-
-
 /* ----------
- * PgStat_MsgHdr                The common message header
- * ----------
- */
-typedef struct PgStat_MsgHdr
-{
-    StatMsgType m_type;
-    int            m_size;
-} PgStat_MsgHdr;
-
-/* ----------
- * Space available in a message.  This will keep the UDP packets below 1K,
- * which should fit unfragmented into the MTU of the loopback interface.
- * (Larger values of PGSTAT_MAX_MSG_SIZE would work for that on most
- * platforms, but we're being conservative here.)
- * ----------
- */
-#define PGSTAT_MAX_MSG_SIZE 1000
-#define PGSTAT_MSG_PAYLOAD    (PGSTAT_MAX_MSG_SIZE - sizeof(PgStat_MsgHdr))
-
-
-/* ----------
- * PgStat_MsgDummy                A dummy message, ignored by the collector
- * ----------
- */
-typedef struct PgStat_MsgDummy
-{
-    PgStat_MsgHdr m_hdr;
-} PgStat_MsgDummy;
-
-
-/* ----------
- * PgStat_MsgInquiry            Sent by a backend to ask the collector
- *                                to write the stats file(s).
- *
- * Ordinarily, an inquiry message prompts writing of the global stats file,
- * the stats file for shared catalogs, and the stats file for the specified
- * database.  If databaseid is InvalidOid, only the first two are written.
- *
- * New file(s) will be written only if the existing file has a timestamp
- * older than the specified cutoff_time; this prevents duplicated effort
- * when multiple requests arrive at nearly the same time, assuming that
- * backends send requests with cutoff_times a little bit in the past.
- *
- * clock_time should be the requestor's current local time; the collector
- * uses this to check for the system clock going backward, but it has no
- * effect unless that occurs.  We assume clock_time >= cutoff_time, though.
- * ----------
- */
-
-typedef struct PgStat_MsgInquiry
-{
-    PgStat_MsgHdr m_hdr;
-    TimestampTz clock_time;        /* observed local clock time */
-    TimestampTz cutoff_time;    /* minimum acceptable file timestamp */
-    Oid            databaseid;        /* requested DB (InvalidOid => shared only) */
-} PgStat_MsgInquiry;
-
-
-/* ----------
- * PgStat_TableEntry            Per-table info in a MsgTabstat
- * ----------
- */
-typedef struct PgStat_TableEntry
-{
-    Oid            t_id;
-    PgStat_TableCounts t_counts;
-} PgStat_TableEntry;
-
-/* ----------
- * PgStat_MsgTabstat            Sent by the backend to report table
- *                                and buffer access statistics.
- * ----------
- */
-#define PGSTAT_NUM_TABENTRIES  \
-    ((PGSTAT_MSG_PAYLOAD - sizeof(Oid) - 3 * sizeof(int) - 2 * sizeof(PgStat_Counter))    \
-     / sizeof(PgStat_TableEntry))
-
-typedef struct PgStat_MsgTabstat
-{
-    PgStat_MsgHdr m_hdr;
-    Oid            m_databaseid;
-    int            m_nentries;
-    int            m_xact_commit;
-    int            m_xact_rollback;
-    PgStat_Counter m_block_read_time;    /* times in microseconds */
-    PgStat_Counter m_block_write_time;
-    PgStat_TableEntry m_entry[PGSTAT_NUM_TABENTRIES];
-} PgStat_MsgTabstat;
-
-
-/* ----------
- * PgStat_MsgTabpurge            Sent by the backend to tell the collector
- *                                about dead tables.
- * ----------
- */
-#define PGSTAT_NUM_TABPURGE  \
-    ((PGSTAT_MSG_PAYLOAD - sizeof(Oid) - sizeof(int))  \
-     / sizeof(Oid))
-
-typedef struct PgStat_MsgTabpurge
-{
-    PgStat_MsgHdr m_hdr;
-    Oid            m_databaseid;
-    int            m_nentries;
-    Oid            m_tableid[PGSTAT_NUM_TABPURGE];
-} PgStat_MsgTabpurge;
-
-
-/* ----------
- * PgStat_MsgDropdb                Sent by the backend to tell the collector
- *                                about a dropped database
- * ----------
- */
-typedef struct PgStat_MsgDropdb
-{
-    PgStat_MsgHdr m_hdr;
-    Oid            m_databaseid;
-} PgStat_MsgDropdb;
-
-
-/* ----------
- * PgStat_MsgResetcounter        Sent by the backend to tell the collector
- *                                to reset counters
- * ----------
- */
-typedef struct PgStat_MsgResetcounter
-{
-    PgStat_MsgHdr m_hdr;
-    Oid            m_databaseid;
-} PgStat_MsgResetcounter;
-
-/* ----------
- * PgStat_MsgResetsharedcounter Sent by the backend to tell the collector
- *                                to reset a shared counter
- * ----------
- */
-typedef struct PgStat_MsgResetsharedcounter
-{
-    PgStat_MsgHdr m_hdr;
-    PgStat_Shared_Reset_Target m_resettarget;
-} PgStat_MsgResetsharedcounter;
-
-/* ----------
- * PgStat_MsgResetsinglecounter Sent by the backend to tell the collector
- *                                to reset a single counter
- * ----------
- */
-typedef struct PgStat_MsgResetsinglecounter
-{
-    PgStat_MsgHdr m_hdr;
-    Oid            m_databaseid;
-    PgStat_Single_Reset_Type m_resettype;
-    Oid            m_objectid;
-} PgStat_MsgResetsinglecounter;
-
-/* ----------
- * PgStat_MsgAutovacStart        Sent by the autovacuum daemon to signal
- *                                that a database is going to be processed
- * ----------
- */
-typedef struct PgStat_MsgAutovacStart
-{
-    PgStat_MsgHdr m_hdr;
-    Oid            m_databaseid;
-    TimestampTz m_start_time;
-} PgStat_MsgAutovacStart;
-
-
-/* ----------
- * PgStat_MsgVacuum                Sent by the backend or autovacuum daemon
- *                                after VACUUM
- * ----------
- */
-typedef struct PgStat_MsgVacuum
-{
-    PgStat_MsgHdr m_hdr;
-    Oid            m_databaseid;
-    Oid            m_tableoid;
-    bool        m_autovacuum;
-    TimestampTz m_vacuumtime;
-    PgStat_Counter m_live_tuples;
-    PgStat_Counter m_dead_tuples;
-} PgStat_MsgVacuum;
-
-
-/* ----------
- * PgStat_MsgAnalyze            Sent by the backend or autovacuum daemon
- *                                after ANALYZE
- * ----------
- */
-typedef struct PgStat_MsgAnalyze
-{
-    PgStat_MsgHdr m_hdr;
-    Oid            m_databaseid;
-    Oid            m_tableoid;
-    bool        m_autovacuum;
-    bool        m_resetcounter;
-    TimestampTz m_analyzetime;
-    PgStat_Counter m_live_tuples;
-    PgStat_Counter m_dead_tuples;
-} PgStat_MsgAnalyze;
-
-
-/* ----------
- * PgStat_MsgArchiver            Sent by the archiver to update statistics.
- * ----------
- */
-typedef struct PgStat_MsgArchiver
-{
-    PgStat_MsgHdr m_hdr;
-    bool        m_failed;        /* Failed attempt */
-    char        m_xlog[MAX_XFN_CHARS + 1];
-    TimestampTz m_timestamp;
-} PgStat_MsgArchiver;
-
-/* ----------
- * PgStat_MsgBgWriter            Sent by the bgwriter to update statistics.
+ * PgStat_MsgBgWriter            bgwriter statistics
  * ----------
  */
 typedef struct PgStat_MsgBgWriter
 {
-    PgStat_MsgHdr m_hdr;
-
     PgStat_Counter m_timed_checkpoints;
     PgStat_Counter m_requested_checkpoints;
     PgStat_Counter m_buf_written_checkpoints;
@@ -422,38 +166,14 @@ typedef struct PgStat_MsgBgWriter
     PgStat_Counter m_checkpoint_sync_time;
 } PgStat_MsgBgWriter;
 
-/* ----------
- * PgStat_MsgRecoveryConflict    Sent by the backend upon recovery conflict
- * ----------
- */
-typedef struct PgStat_MsgRecoveryConflict
-{
-    PgStat_MsgHdr m_hdr;
-
-    Oid            m_databaseid;
-    int            m_reason;
-} PgStat_MsgRecoveryConflict;
-
-/* ----------
- * PgStat_MsgTempFile    Sent by the backend upon creating a temp file
- * ----------
- */
-typedef struct PgStat_MsgTempFile
-{
-    PgStat_MsgHdr m_hdr;
-
-    Oid            m_databaseid;
-    size_t        m_filesize;
-} PgStat_MsgTempFile;
-
 /* ----------
  * PgStat_FunctionCounts    The actual per-function counts kept by a backend
  *
  * This struct should contain only actual event counters, because we memcmp
- * it against zeroes to detect whether there are any counts to transmit.
+ * it against zeroes to detect whether there are any counts to apply.
  *
  * Note that the time counters are in instr_time format here.  We convert to
- * microseconds in PgStat_Counter format when transmitting to the collector.
+ * microseconds in PgStat_Counter format when applying to shared statsitics.
  * ----------
  */
 typedef struct PgStat_FunctionCounts
@@ -485,81 +205,8 @@ typedef struct PgStat_FunctionEntry
     PgStat_Counter f_self_time;
 } PgStat_FunctionEntry;
 
-/* ----------
- * PgStat_MsgFuncstat            Sent by the backend to report function
- *                                usage statistics.
- * ----------
- */
-#define PGSTAT_NUM_FUNCENTRIES    \
-    ((PGSTAT_MSG_PAYLOAD - sizeof(Oid) - sizeof(int))  \
-     / sizeof(PgStat_FunctionEntry))
-
-typedef struct PgStat_MsgFuncstat
-{
-    PgStat_MsgHdr m_hdr;
-    Oid            m_databaseid;
-    int            m_nentries;
-    PgStat_FunctionEntry m_entry[PGSTAT_NUM_FUNCENTRIES];
-} PgStat_MsgFuncstat;
-
-/* ----------
- * PgStat_MsgFuncpurge            Sent by the backend to tell the collector
- *                                about dead functions.
- * ----------
- */
-#define PGSTAT_NUM_FUNCPURGE  \
-    ((PGSTAT_MSG_PAYLOAD - sizeof(Oid) - sizeof(int))  \
-     / sizeof(Oid))
-
-typedef struct PgStat_MsgFuncpurge
-{
-    PgStat_MsgHdr m_hdr;
-    Oid            m_databaseid;
-    int            m_nentries;
-    Oid            m_functionid[PGSTAT_NUM_FUNCPURGE];
-} PgStat_MsgFuncpurge;
-
-/* ----------
- * PgStat_MsgDeadlock            Sent by the backend to tell the collector
- *                                about a deadlock that occurred.
- * ----------
- */
-typedef struct PgStat_MsgDeadlock
-{
-    PgStat_MsgHdr m_hdr;
-    Oid            m_databaseid;
-} PgStat_MsgDeadlock;
-
-
-/* ----------
- * PgStat_Msg                    Union over all possible messages.
- * ----------
- */
-typedef union PgStat_Msg
-{
-    PgStat_MsgHdr msg_hdr;
-    PgStat_MsgDummy msg_dummy;
-    PgStat_MsgInquiry msg_inquiry;
-    PgStat_MsgTabstat msg_tabstat;
-    PgStat_MsgTabpurge msg_tabpurge;
-    PgStat_MsgDropdb msg_dropdb;
-    PgStat_MsgResetcounter msg_resetcounter;
-    PgStat_MsgResetsharedcounter msg_resetsharedcounter;
-    PgStat_MsgResetsinglecounter msg_resetsinglecounter;
-    PgStat_MsgAutovacStart msg_autovacuum;
-    PgStat_MsgVacuum msg_vacuum;
-    PgStat_MsgAnalyze msg_analyze;
-    PgStat_MsgArchiver msg_archiver;
-    PgStat_MsgBgWriter msg_bgwriter;
-    PgStat_MsgFuncstat msg_funcstat;
-    PgStat_MsgFuncpurge msg_funcpurge;
-    PgStat_MsgRecoveryConflict msg_recoveryconflict;
-    PgStat_MsgDeadlock msg_deadlock;
-} PgStat_Msg;
-
-
 /* ------------------------------------------------------------
- * Statistic collector data structures follow
+ * Statistic collector data structures on file and shared memory follow
  *
  * PGSTAT_FILE_FORMAT_ID should be changed whenever any of these
  * data structures change.
@@ -568,6 +215,12 @@ typedef union PgStat_Msg
 
 #define PGSTAT_FILE_FORMAT_ID    0x01A5BC9D
 
+typedef struct PgStat_DSHash
+{
+    int        refcnt;
+    dshash_table_handle handle;
+} PgStat_DSHash;
+
 /* ----------
  * PgStat_StatDBEntry            The collector's data per database
  * ----------
@@ -597,17 +250,22 @@ typedef struct PgStat_StatDBEntry
     PgStat_Counter n_block_write_time;
 
     TimestampTz stat_reset_timestamp;
-    TimestampTz stats_timestamp;    /* time of db stats file update */
+    TimestampTz stats_timestamp;        /* time of db stats  update */
 
     /*
-     * tables and functions must be last in the struct, because we don't write
-     * the pointers out to the stats file.
+     * The followings must be last in the struct, because we don't write them
+     * out to the stats file.
      */
-    HTAB       *tables;
-    HTAB       *functions;
+    int generation;                        /* current generation of the below */
+    int    refcnt;                            /* current gen reference count */
+    dshash_table_handle tables;            /* current gen tables hash */
+    dshash_table_handle functions;        /* current gen functions hash */
+    int    prev_refcnt;                    /* prev gen reference count */
+    dshash_table_handle prev_tables;    /* prev gen tables hash */
+    dshash_table_handle prev_functions;    /* prev gen functions hash */
+    LWLock    lock;                        /* Lock for the above members */
 } PgStat_StatDBEntry;
 
-
 /* ----------
  * PgStat_StatTabEntry            The collector's data per table (or index)
  * ----------
@@ -645,7 +303,7 @@ typedef struct PgStat_StatTabEntry
 
 
 /* ----------
- * PgStat_StatFuncEntry            The collector's data per function
+ * PgStat_StatFuncEntry            per function stats data
  * ----------
  */
 typedef struct PgStat_StatFuncEntry
@@ -660,7 +318,7 @@ typedef struct PgStat_StatFuncEntry
 
 
 /*
- * Archiver statistics kept in the stats collector
+ * Archiver statistics kept in the shared stats
  */
 typedef struct PgStat_ArchiverStats
 {
@@ -676,7 +334,7 @@ typedef struct PgStat_ArchiverStats
 } PgStat_ArchiverStats;
 
 /*
- * Global statistics kept in the stats collector
+ * Global statistics kept in the shared stats
  */
 typedef struct PgStat_GlobalStats
 {
@@ -762,7 +420,6 @@ typedef enum
     WAIT_EVENT_CHECKPOINTER_MAIN,
     WAIT_EVENT_LOGICAL_APPLY_MAIN,
     WAIT_EVENT_LOGICAL_LAUNCHER_MAIN,
-    WAIT_EVENT_PGSTAT_MAIN,
     WAIT_EVENT_RECOVERY_WAL_ALL,
     WAIT_EVENT_RECOVERY_WAL_STREAM,
     WAIT_EVENT_SYSLOGGER_MAIN,
@@ -1146,6 +803,8 @@ extern bool pgstat_track_counts;
 extern int    pgstat_track_functions;
 extern PGDLLIMPORT int pgstat_track_activity_query_size;
 extern char *pgstat_stat_directory;
+
+/* No longer used, but will be removed with GUC */
 extern char *pgstat_stat_tmpname;
 extern char *pgstat_stat_filename;
 
@@ -1167,31 +826,29 @@ extern PgStat_Counter pgStatBlockWriteTime;
 extern Size BackendStatusShmemSize(void);
 extern void CreateSharedBackendStatus(void);
 
-extern void pgstat_init(void);
-extern int    pgstat_start(void);
+extern void pgstat_initialize(void);
+extern Size StatsShmemSize(void);
+extern void StatsShmemInit(void);
+
 extern void pgstat_reset_all(void);
-extern void allow_immediate_pgstat_restart(void);
-
-#ifdef EXEC_BACKEND
-extern void PgstatCollectorMain(int argc, char *argv[]) pg_attribute_noreturn();
-#endif
 
+/* File input/output functions  */
+extern void pgstat_read_statsfiles(void);
+extern void pgstat_write_statsfiles(void);
 
 /* ----------
  * Functions called from backends
  * ----------
  */
-extern void pgstat_ping(void);
-
-extern void pgstat_report_stat(bool force);
+extern long pgstat_report_stat(bool force);
 extern void pgstat_vacuum_stat(void);
 extern void pgstat_drop_database(Oid databaseid);
 
 extern void pgstat_clear_snapshot(void);
 extern void pgstat_reset_counters(void);
-extern void pgstat_reset_shared_counters(const char *);
-extern void pgstat_reset_single_counter(Oid objectid, PgStat_Single_Reset_Type type);
-
+extern void pgstat_reset_shared_counters(const char *target);
+extern void pgstat_reset_single_counter(Oid objectid,
+                                        PgStat_Single_Reset_Type type);
 extern void pgstat_report_autovac(Oid dboid);
 extern void pgstat_report_vacuum(Oid tableoid, bool shared,
                      PgStat_Counter livetuples, PgStat_Counter deadtuples);
@@ -1202,26 +859,10 @@ extern void pgstat_report_analyze(Relation rel,
 extern void pgstat_report_recovery_conflict(int reason);
 extern void pgstat_report_deadlock(void);
 
-extern void pgstat_initialize(void);
 extern void pgstat_bestart(void);
-
 extern void pgstat_report_activity(BackendState state, const char *cmd_str);
-extern void pgstat_report_tempfile(size_t filesize);
-extern void pgstat_report_appname(const char *appname);
-extern void pgstat_report_xact_timestamp(TimestampTz tstamp);
-extern const char *pgstat_get_wait_event(uint32 wait_event_info);
-extern const char *pgstat_get_wait_event_type(uint32 wait_event_info);
-extern const char *pgstat_get_backend_current_activity(int pid, bool checkUser);
-extern const char *pgstat_get_crashed_backend_activity(int pid, char *buffer,
-                                    int buflen);
-extern const char *pgstat_get_backend_desc(BackendType backendType);
 
-extern void pgstat_progress_start_command(ProgressCommandType cmdtype,
-                              Oid relid);
-extern void pgstat_progress_update_param(int index, int64 val);
-extern void pgstat_progress_update_multi_param(int nparam, const int *index,
-                                   const int64 *val);
-extern void pgstat_progress_end_command(void);
+extern void pgstat_report_tempfile(size_t filesize);
 
 extern PgStat_TableStatus *find_tabstat_entry(Oid rel_id);
 extern PgStat_BackendFunctionEntry *find_funcstat_entry(Oid func_id);
@@ -1351,18 +992,38 @@ extern void pgstat_twophase_postabort(TransactionId xid, uint16 info,
 extern void pgstat_send_archiver(const char *xlog, bool failed);
 extern void pgstat_send_bgwriter(void);
 
+
+
+extern PgStat_StatDBEntry *pgstat_fetch_stat_dbentry(Oid relid);
+
+extern void pgstat_report_appname(const char *appname);
+extern void pgstat_report_xact_timestamp(TimestampTz tstamp);
+extern const char *pgstat_get_wait_event(uint32 wait_event_info);
+extern const char *pgstat_get_wait_event_type(uint32 wait_event_info);
+extern const char *pgstat_get_backend_current_activity(int pid, bool checkUser);
+extern const char *pgstat_get_crashed_backend_activity(int pid, char *buffer,
+                                    int buflen);
+extern const char *pgstat_get_backend_desc(BackendType backendType);
+
+extern void pgstat_progress_start_command(ProgressCommandType cmdtype,
+                              Oid relid);
+extern void pgstat_progress_update_param(int index, int64 val);
+extern void pgstat_progress_update_multi_param(int nparam, const int *index,
+                                   const int64 *val);
+extern void pgstat_progress_end_command(void);
 /* ----------
  * Support functions for the SQL-callable functions to
  * generate the pgstat* views.
  * ----------
  */
-extern PgStat_StatDBEntry *pgstat_fetch_stat_dbentry(Oid dbid);
+extern void pgstat_clear_snapshot(void);
 extern PgStat_StatTabEntry *pgstat_fetch_stat_tabentry(Oid relid);
-extern PgBackendStatus *pgstat_fetch_stat_beentry(int beid);
-extern LocalPgBackendStatus *pgstat_fetch_stat_local_beentry(int beid);
+extern PgStat_StatTabEntry *pgstat_fetch_stat_tabentry_extended(PgStat_StatDBEntry *dbent, Oid relid);
 extern PgStat_StatFuncEntry *pgstat_fetch_stat_funcentry(Oid funcid);
-extern int    pgstat_fetch_stat_numbackends(void);
 extern PgStat_ArchiverStats *pgstat_fetch_stat_archiver(void);
 extern PgStat_GlobalStats *pgstat_fetch_global(void);
 
+extern PgBackendStatus *pgstat_fetch_stat_beentry(int beid);
+extern int    pgstat_fetch_stat_numbackends(void);
+extern LocalPgBackendStatus *pgstat_fetch_stat_local_beentry(int beid);
 #endif                            /* PGSTAT_H */
diff --git a/src/include/storage/lwlock.h b/src/include/storage/lwlock.h
index 96c7732006..e2277d67a3 100644
--- a/src/include/storage/lwlock.h
+++ b/src/include/storage/lwlock.h
@@ -219,6 +219,7 @@ typedef enum BuiltinTrancheIds
     LWTRANCHE_SHARED_TUPLESTORE,
     LWTRANCHE_TBM,
     LWTRANCHE_PARALLEL_APPEND,
+    LWTRANCHE_STATS,
     LWTRANCHE_FIRST_USER_DEFINED
 }            BuiltinTrancheIds;
 
diff --git a/src/include/utils/timeout.h b/src/include/utils/timeout.h
index 9244a2a7b7..a9b625211b 100644
--- a/src/include/utils/timeout.h
+++ b/src/include/utils/timeout.h
@@ -31,6 +31,7 @@ typedef enum TimeoutId
     STANDBY_TIMEOUT,
     STANDBY_LOCK_TIMEOUT,
     IDLE_IN_TRANSACTION_SESSION_TIMEOUT,
+    IDLE_STATS_UPDATE_TIMEOUT,
     /* First user-definable timeout reason */
     USER_TIMEOUT,
     /* Maximum number of timeout reasons */
-- 
2.16.3

From 969528ea377452681fe38af9ce797eeb68742af6 Mon Sep 17 00:00:00 2001
From: Kyotaro Horiguchi <horiguchi.kyotaro@lab.ntt.co.jp>
Date: Tue, 27 Nov 2018 14:42:12 +0900
Subject: [PATCH 6/6] Remove the GUC stats_temp_directory

The guc used to specifie the directory to store temporary statistics
files. It is no longer needed by the stats collector but still used by
the programs in bin and contirb, and maybe other extensions. Thus this
patch removes the GUC but some backing variables and macro definitions
are left alone for backward comptibility.
---
 doc/src/sgml/backup.sgml                      |  2 --
 doc/src/sgml/config.sgml                      | 19 -------------
 doc/src/sgml/monitoring.sgml                  |  7 +----
 doc/src/sgml/storage.sgml                     |  3 +-
 src/backend/postmaster/pgstat.c               | 13 ++++-----
 src/backend/replication/basebackup.c          | 13 ++-------
 src/backend/utils/misc/guc.c                  | 41 ---------------------------
 src/backend/utils/misc/postgresql.conf.sample |  1 -
 src/include/pgstat.h                          |  5 +++-
 9 files changed, 14 insertions(+), 90 deletions(-)

diff --git a/doc/src/sgml/backup.sgml b/doc/src/sgml/backup.sgml
index a73fd4d044..95285809c2 100644
--- a/doc/src/sgml/backup.sgml
+++ b/doc/src/sgml/backup.sgml
@@ -1119,8 +1119,6 @@ SELECT pg_stop_backup();
     <filename>pg_snapshots/</filename>, <filename>pg_stat_tmp/</filename>,
     and <filename>pg_subtrans/</filename> (but not the directories themselves) can be
     omitted from the backup as they will be initialized on postmaster startup.
-    If <xref linkend="guc-stats-temp-directory"/> is set and is under the data
-    directory then the contents of that directory can also be omitted.
    </para>
 
    <para>
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 8bd57f376b..79f704cc99 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -6709,25 +6709,6 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
       </listitem>
      </varlistentry>
 
-     <varlistentry id="guc-stats-temp-directory" xreflabel="stats_temp_directory">
-      <term><varname>stats_temp_directory</varname> (<type>string</type>)
-      <indexterm>
-       <primary><varname>stats_temp_directory</varname> configuration parameter</primary>
-      </indexterm>
-      </term>
-      <listitem>
-       <para>
-        Sets the directory to store temporary statistics data in. This can be
-        a path relative to the data directory or an absolute path. The default
-        is <filename>pg_stat_tmp</filename>. Pointing this at a RAM-based
-        file system will decrease physical I/O requirements and can lead to
-        improved performance.
-        This parameter can only be set in the <filename>postgresql.conf</filename>
-        file or on the server command line.
-       </para>
-      </listitem>
-     </varlistentry>
-
      </variablelist>
     </sect2>
 
diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 83a0be1965..bf94bd87d2 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -195,12 +195,7 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
 
   <para>
    The statistics collector transmits the collected information to other
-   <productname>PostgreSQL</productname> processes through temporary files.
-   These files are stored in the directory named by the
-   <xref linkend="guc-stats-temp-directory"/> parameter,
-   <filename>pg_stat_tmp</filename> by default.
-   For better performance, <varname>stats_temp_directory</varname> can be
-   pointed at a RAM-based file system, decreasing physical I/O requirements.
+   <productname>PostgreSQL</productname> processes through shared memory.
    When the server shuts down cleanly, a permanent copy of the statistics
    data is stored in the <filename>pg_stat</filename> subdirectory, so that
    statistics can be retained across server restarts.  When recovery is
diff --git a/doc/src/sgml/storage.sgml b/doc/src/sgml/storage.sgml
index cbdad0c3fb..133eb3ff19 100644
--- a/doc/src/sgml/storage.sgml
+++ b/doc/src/sgml/storage.sgml
@@ -122,8 +122,7 @@ Item
 
 <row>
  <entry><filename>pg_stat_tmp</filename></entry>
- <entry>Subdirectory containing temporary files for the statistics
-  subsystem</entry>
+ <entry>Subdirectory containing ephemeral files for extensions</entry>
 </row>
 
 <row>
diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index ba4c274f9a..8f8ac0b356 100644
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -102,15 +102,12 @@ bool        pgstat_track_counts = false;
 int            pgstat_track_functions = TRACK_FUNC_OFF;
 int            pgstat_track_activity_query_size = 1024;
 
-/* ----------
- * Built from GUC parameter
- * ----------
+/*
+ * This used to be a GUC variable and is no longer used in this file, but left
+ * alone just for backward comptibility for extensions, having the default
+ * value.
  */
-char       *pgstat_stat_directory = NULL;
-
-/* No longer used, but will be removed with GUC */
-char       *pgstat_stat_filename = NULL;
-char       *pgstat_stat_tmpname = NULL;
+char       *pgstat_stat_directory = PG_STAT_TMP_DIR;
 
 LWLock        StatsMainLock;
 #define        StatsLock (&StatsMainLock)
diff --git a/src/backend/replication/basebackup.c b/src/backend/replication/basebackup.c
index def6c03dd0..58ba33e822 100644
--- a/src/backend/replication/basebackup.c
+++ b/src/backend/replication/basebackup.c
@@ -230,11 +230,8 @@ perform_base_backup(basebackup_options *opt)
     TimeLineID    endtli;
     StringInfo    labelfile;
     StringInfo    tblspc_map_file = NULL;
-    int            datadirpathlen;
     List       *tablespaces = NIL;
 
-    datadirpathlen = strlen(DataDir);
-
     backup_started_in_recovery = RecoveryInProgress();
 
     labelfile = makeStringInfo();
@@ -265,13 +262,9 @@ perform_base_backup(basebackup_options *opt)
          * Calculate the relative path of temporary statistics directory in
          * order to skip the files which are located in that directory later.
          */
-        if (is_absolute_path(pgstat_stat_directory) &&
-            strncmp(pgstat_stat_directory, DataDir, datadirpathlen) == 0)
-            statrelpath = psprintf("./%s", pgstat_stat_directory + datadirpathlen + 1);
-        else if (strncmp(pgstat_stat_directory, "./", 2) != 0)
-            statrelpath = psprintf("./%s", pgstat_stat_directory);
-        else
-            statrelpath = pgstat_stat_directory;
+
+        Assert(strchr(PG_STAT_TMP_DIR, '/') == NULL);
+        statrelpath = psprintf("./%s", PG_STAT_TMP_DIR);
 
         /* Add a node for the base directory at the end */
         ti = palloc0(sizeof(tablespaceinfo));
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 156d147c85..058d97075f 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -191,7 +191,6 @@ static bool check_max_wal_senders(int *newval, void **extra, GucSource source);
 static bool check_autovacuum_work_mem(int *newval, void **extra, GucSource source);
 static bool check_effective_io_concurrency(int *newval, void **extra, GucSource source);
 static void assign_effective_io_concurrency(int newval, void *extra);
-static void assign_pgstat_temp_directory(const char *newval, void *extra);
 static bool check_application_name(char **newval, void **extra, GucSource source);
 static void assign_application_name(const char *newval, void *extra);
 static bool check_cluster_name(char **newval, void **extra, GucSource source);
@@ -3988,17 +3987,6 @@ static struct config_string ConfigureNamesString[] =
         NULL, NULL, NULL
     },
 
-    {
-        {"stats_temp_directory", PGC_SIGHUP, STATS_COLLECTOR,
-            gettext_noop("Writes temporary statistics files to the specified directory."),
-            NULL,
-            GUC_SUPERUSER_ONLY
-        },
-        &pgstat_temp_directory,
-        PG_STAT_TMP_DIR,
-        check_canonical_path, assign_pgstat_temp_directory, NULL
-    },
-
     {
         {"synchronous_standby_names", PGC_SIGHUP, REPLICATION_MASTER,
             gettext_noop("Number of synchronous standbys and list of names of potential synchronous ones."),
@@ -11002,35 +10990,6 @@ assign_effective_io_concurrency(int newval, void *extra)
 #endif                            /* USE_PREFETCH */
 }
 
-static void
-assign_pgstat_temp_directory(const char *newval, void *extra)
-{
-    /* check_canonical_path already canonicalized newval for us */
-    char       *dname;
-    char       *tname;
-    char       *fname;
-
-    /* directory */
-    dname = guc_malloc(ERROR, strlen(newval) + 1);    /* runtime dir */
-    sprintf(dname, "%s", newval);
-
-    /* global stats */
-    tname = guc_malloc(ERROR, strlen(newval) + 12); /* /global.tmp */
-    sprintf(tname, "%s/global.tmp", newval);
-    fname = guc_malloc(ERROR, strlen(newval) + 13); /* /global.stat */
-    sprintf(fname, "%s/global.stat", newval);
-
-    if (pgstat_stat_directory)
-        free(pgstat_stat_directory);
-    pgstat_stat_directory = dname;
-    if (pgstat_stat_tmpname)
-        free(pgstat_stat_tmpname);
-    pgstat_stat_tmpname = tname;
-    if (pgstat_stat_filename)
-        free(pgstat_stat_filename);
-    pgstat_stat_filename = fname;
-}
-
 static bool
 check_application_name(char **newval, void **extra, GucSource source)
 {
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 194f312096..fdb088dbfd 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -554,7 +554,6 @@
 #track_io_timing = off
 #track_functions = none            # none, pl, all
 #track_activity_query_size = 1024    # (change requires restart)
-#stats_temp_directory = 'pg_stat_tmp'
 
 
 # - Monitoring -
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index cb70d00b8f..265ed4d118 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -31,7 +31,10 @@
 #define PGSTAT_STAT_PERMANENT_FILENAME        "pg_stat/global.stat"
 #define PGSTAT_STAT_PERMANENT_TMPFILE        "pg_stat/global.tmp"
 
-/* Default directory to store temporary statistics data in */
+/*
+ * This used to be the directory to store temporary statistics data in but is
+ * no longer used. Defined here for backward compatibility.
+ */
 #define PG_STAT_TMP_DIR        "pg_stat_tmp"
 
 /* Values for track_functions GUC variable --- order is significant! */
-- 
2.16.3


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