Let's remove DSM_IMPL_NONE.

Hello.

# Subject is fixed.

I think this kind of thing is sutable for doing at the beginning
of a dev cycle.

Since it has been a long time since DSM was introduced and it is
turned on by default and I believe no one turns it off on
purpose. I'd like to propose to get rid of the choice of none.

The motive of this is there's a case where fallback path is
large(?) but scarcely expected to be used.


regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center
From 3322194ecf9c9dc02f1f96f71abc421cd65ff1eb Mon Sep 17 00:00:00 2001
From: Kyotaro Horiguchi <horiguchi.kyotaro@lab.ntt.co.jp>
Date: Thu, 15 Feb 2018 11:22:50 +0900
Subject: [PATCH] Remove dynamic_shared_memroy_type=none

Nowadays PostgreSQL on all supported platform offers any kind of
dynamic shared memory feature. Assuming none hinder us from using it
for core features.  Just removing the option leads to intermittent
failure of regression test on some platforms due to insufficient
max_connection on initdb. This patch requires the patch that increases
the minimum fallback value of max_connection of initdb.
---
 doc/src/sgml/config.sgml                      |  6 +++---
 src/backend/access/transam/parallel.c         |  7 -------
 src/backend/optimizer/plan/planner.c          |  4 +---
 src/backend/storage/ipc/dsm.c                 | 15 ---------------
 src/backend/storage/ipc/dsm_impl.c            |  3 ---
 src/backend/utils/misc/postgresql.conf.sample |  1 -
 src/bin/initdb/initdb.c                       | 21 ++++++++++++++-------
 src/include/storage/dsm_impl.h                |  9 ++++-----
 8 files changed, 22 insertions(+), 44 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 7bfbc87109..68ca92d591 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -1662,9 +1662,9 @@ include_dir 'conf.d'
         should use.  Possible values are <literal>posix</literal> (for POSIX shared
         memory allocated using <literal>shm_open</literal>), <literal>sysv</literal>
         (for System V shared memory allocated via <literal>shmget</literal>),
-        <literal>windows</literal> (for Windows shared memory), <literal>mmap</literal>
-        (to simulate shared memory using memory-mapped files stored in the
-        data directory), and <literal>none</literal> (to disable this feature).
+        <literal>windows</literal> (for Windows shared memory),
+        and <literal>mmap</literal> (to simulate shared memory using
+        memory-mapped files stored in the data directory).
         Not all values are supported on all platforms; the first supported
         option is the default for that platform.  The use of the
         <literal>mmap</literal> option, which is not the default on any platform,
diff --git a/src/backend/access/transam/parallel.c b/src/backend/access/transam/parallel.c
index 1d631b7275..4e32cfff50 100644
--- a/src/backend/access/transam/parallel.c
+++ b/src/backend/access/transam/parallel.c
@@ -161,13 +161,6 @@ CreateParallelContext(const char *library_name, const char *function_name,
     /* Number of workers should be non-negative. */
     Assert(nworkers >= 0);
 
-    /*
-     * If dynamic shared memory is not available, we won't be able to use
-     * background workers.
-     */
-    if (dynamic_shared_memory_type == DSM_IMPL_NONE)
-        nworkers = 0;
-
     /*
      * If we are running under serializable isolation, we can't use parallel
      * workers, at least not until somebody enhances that mechanism to be
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 1f09fb6e6a..86b7b74129 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -335,7 +335,6 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
      */
     if ((cursorOptions & CURSOR_OPT_PARALLEL_OK) != 0 &&
         IsUnderPostmaster &&
-        dynamic_shared_memory_type != DSM_IMPL_NONE &&
         parse->commandType == CMD_SELECT &&
         !parse->hasModifyingCTE &&
         max_parallel_workers_per_gather > 0 &&
@@ -6046,8 +6045,7 @@ plan_create_index_workers(Oid tableOid, Oid indexOid)
     double        allvisfrac;
 
     /* Return immediately when parallelism disabled */
-    if (dynamic_shared_memory_type == DSM_IMPL_NONE ||
-        max_parallel_maintenance_workers == 0)
+    if (max_parallel_maintenance_workers == 0)
         return 0;
 
     /* Set up largely-dummy planner state */
diff --git a/src/backend/storage/ipc/dsm.c b/src/backend/storage/ipc/dsm.c
index f1f75b73f5..9629f22f7a 100644
--- a/src/backend/storage/ipc/dsm.c
+++ b/src/backend/storage/ipc/dsm.c
@@ -150,10 +150,6 @@ dsm_postmaster_startup(PGShmemHeader *shim)
 
     Assert(!IsUnderPostmaster);
 
-    /* If dynamic shared memory is disabled, there's nothing to do. */
-    if (dynamic_shared_memory_type == DSM_IMPL_NONE)
-        return;
-
     /*
      * If we're using the mmap implementations, clean up any leftovers.
      * Cleanup isn't needed on Windows, and happens earlier in startup for
@@ -219,10 +215,6 @@ dsm_cleanup_using_control_segment(dsm_handle old_control_handle)
     uint32        i;
     dsm_control_header *old_control;
 
-    /* If dynamic shared memory is disabled, there's nothing to do. */
-    if (dynamic_shared_memory_type == DSM_IMPL_NONE)
-        return;
-
     /*
      * Try to attach the segment.  If this fails, it probably just means that
      * the operating system has been rebooted and the segment no longer
@@ -391,13 +383,6 @@ dsm_postmaster_shutdown(int code, Datum arg)
 static void
 dsm_backend_startup(void)
 {
-    /* If dynamic shared memory is disabled, reject this. */
-    if (dynamic_shared_memory_type == DSM_IMPL_NONE)
-        ereport(ERROR,
-                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-                 errmsg("dynamic shared memory is disabled"),
-                 errhint("Set dynamic_shared_memory_type to a value other than \"none\".")));
-
 #ifdef EXEC_BACKEND
     {
         void       *control_address = NULL;
diff --git a/src/backend/storage/ipc/dsm_impl.c b/src/backend/storage/ipc/dsm_impl.c
index c6382ec031..77e1bab54b 100644
--- a/src/backend/storage/ipc/dsm_impl.c
+++ b/src/backend/storage/ipc/dsm_impl.c
@@ -106,7 +106,6 @@ const struct config_enum_entry dynamic_shared_memory_options[] = {
 #ifdef USE_DSM_MMAP
     {"mmap", DSM_IMPL_MMAP, false},
 #endif
-    {"none", DSM_IMPL_NONE, false},
     {NULL, 0, false}
 };
 
@@ -210,8 +209,6 @@ dsm_impl_can_resize(void)
 {
     switch (dynamic_shared_memory_type)
     {
-        case DSM_IMPL_NONE:
-            return false;
         case DSM_IMPL_POSIX:
             return true;
         case DSM_IMPL_SYSV:
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 9e39baf466..657c3f81f8 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -133,7 +133,6 @@
                     #   sysv
                     #   windows
                     #   mmap
-                    # use none to disable dynamic shared memory
                     # (change requires restart)
 
 # - Disk -
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index ae22e7d9fb..0233fd4edc 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -984,6 +984,16 @@ test_config_settings(void)
                 ok_buffers = 0;
 
 
+    /*
+     * Server doesn't confirm that the server-default DSM implementation is
+     * actually workable. Choose a fine one for probing then it is used on the
+     * new database.
+     */
+    printf(_("selecting dynamic shared memory implementation ... "));
+    fflush(stdout);
+    dynamic_shared_memory_type = choose_dsm_implementation();
+    printf("%s\n", dynamic_shared_memory_type);
+
     printf(_("selecting default max_connections ... "));
     fflush(stdout);
 
@@ -996,10 +1006,11 @@ test_config_settings(void)
                  "\"%s\" --boot -x0 %s "
                  "-c max_connections=%d "
                  "-c shared_buffers=%d "
-                 "-c dynamic_shared_memory_type=none "
+                 "-c dynamic_shared_memory_type=%s "
                  "< \"%s\" > \"%s\" 2>&1",
                  backend_exec, boot_options,
                  test_conns, test_buffs,
+                 dynamic_shared_memory_type,
                  DEVNULL, DEVNULL);
         status = system(cmd);
         if (status == 0)
@@ -1031,10 +1042,11 @@ test_config_settings(void)
                  "\"%s\" --boot -x0 %s "
                  "-c max_connections=%d "
                  "-c shared_buffers=%d "
-                 "-c dynamic_shared_memory_type=none "
+                 "-c dynamic_shared_memory_type=%s "
                  "< \"%s\" > \"%s\" 2>&1",
                  backend_exec, boot_options,
                  n_connections, test_buffs,
+                 dynamic_shared_memory_type,
                  DEVNULL, DEVNULL);
         status = system(cmd);
         if (status == 0)
@@ -1046,11 +1058,6 @@ test_config_settings(void)
         printf("%dMB\n", (n_buffers * (BLCKSZ / 1024)) / 1024);
     else
         printf("%dkB\n", n_buffers * (BLCKSZ / 1024));
-
-    printf(_("selecting dynamic shared memory implementation ... "));
-    fflush(stdout);
-    dynamic_shared_memory_type = choose_dsm_implementation();
-    printf("%s\n", dynamic_shared_memory_type);
 }
 
 /*
diff --git a/src/include/storage/dsm_impl.h b/src/include/storage/dsm_impl.h
index 0e5730f7c5..2ed1d686b3 100644
--- a/src/include/storage/dsm_impl.h
+++ b/src/include/storage/dsm_impl.h
@@ -14,11 +14,10 @@
 #define DSM_IMPL_H
 
 /* Dynamic shared memory implementations. */
-#define DSM_IMPL_NONE            0
-#define DSM_IMPL_POSIX            1
-#define DSM_IMPL_SYSV            2
-#define DSM_IMPL_WINDOWS        3
-#define DSM_IMPL_MMAP            4
+#define DSM_IMPL_POSIX            0
+#define DSM_IMPL_SYSV            1
+#define DSM_IMPL_WINDOWS        2
+#define DSM_IMPL_MMAP            3
 
 /*
  * Determine which dynamic shared memory implementations will be supported
-- 
2.16.3