Re: Transactions and temp tables

Hi,

Here are the patches for 8.4 (1 patch for the code and 1 patch for the
regression tests).

Thanks in advance for your feedback,
Emmanuel

David Fetter wrote:
> On Tue, Oct 07, 2008 at 06:12:14PM -0400, Emmanuel Cecchet wrote:
>
>> Hi,
>>
>>
>>> On Tue, Oct 07, 2008 at 04:57:37PM -0400, Emmanuel Cecchet wrote:
>>>
>>>
>>>> Heikki,
>>>>
>>>> Here is a new version of the patch using a hash table as you
>>>> suggested.  I also include the tests that I have added to the
>>>> regression test suite  to test the various scenarios.  All patches
>>>> are based on Postgres 8.3.3, let me know if you want me to
>>>> generate patch for 8.4.
>>>>
>>> CVS TIP is the only place where new features, like this, go :)
>>>
>>>
>> I looked at the Wiki and it looks like I should add en entry
>> (assuming I  get a patch for the current CVS HEAD) to CommitFest
>> 2008-11. Is that  correct?
>>
>>
>>> I didn't see the attachment anyhow...
>>>
>>>
>> Good point! The same with the attachments now!
>>
>
> Perhaps we did not make this clear.  The patch is a new feature.  New
> features are not going into 8.3, as it has already been released.
>
> Make a patch against CVS TIP aka 8.4, and re-submit.
>
> Cheers,
> David
>

--
Emmanuel Cecchet
FTO @ Frog Thinker
Open Source Development & Consulting
--
Web: http://www.frogthinker.org
email: manu@frogthinker.org
Skype: emmanuel_cecchet

### Eclipse Workspace Patch 1.0
#P Postgres-HEAD
Index: src/test/regress/parallel_schedule
===================================================================
RCS file: /root/cvsrepo/pgsql/src/test/regress/parallel_schedule,v
retrieving revision 1.46
diff -u -r1.46 parallel_schedule
--- src/test/regress/parallel_schedule    24 Nov 2007 19:49:23 -0000    1.46
+++ src/test/regress/parallel_schedule    7 Oct 2008 23:41:14 -0000
@@ -90,3 +90,11 @@

 # run tablespace by itself
 test: tablespace
+
+# --------
+# 2PC related tests
+# --------
+test: 2pc_persistent_table 2pc_on_delete_rows_transaction 2pc_on_commit_drop 2pc_temp_table_transaction
2pc_temp_table_rollback2pc_temp_table_savepoint 2pc_temp_table_failure 
+test: 2pc_dirty_buffer_check
+test: 2pc_temp_table_session
+test: 2pc_on_delete_rows_session
\ No newline at end of file
Index: src/test/regress/serial_schedule
===================================================================
RCS file: /root/cvsrepo/pgsql/src/test/regress/serial_schedule,v
retrieving revision 1.43
diff -u -r1.43 serial_schedule
--- src/test/regress/serial_schedule    24 Nov 2007 20:41:35 -0000    1.43
+++ src/test/regress/serial_schedule    7 Oct 2008 23:41:14 -0000
@@ -115,3 +115,13 @@
 test: xml
 test: stats
 test: tablespace
+test: 2pc_persistent_table
+test: 2pc_on_delete_rows_transaction
+test: 2pc_on_commit_drop
+test: 2pc_temp_table_transaction
+test: 2pc_temp_table_rollback
+test: 2pc_temp_table_savepoint
+test: 2pc_dirty_buffer_check
+test: 2pc_temp_table_session
+test: 2pc_on_delete_rows_session
+test: 2pc_temp_table_failure
\ No newline at end of file
Index: src/test/regress/sql/2pc_on_delete_rows_transaction.sql
===================================================================
RCS file: src/test/regress/sql/2pc_on_delete_rows_transaction.sql
diff -N src/test/regress/sql/2pc_on_delete_rows_transaction.sql
--- /dev/null    1 Jan 1970 00:00:00 -0000
+++ src/test/regress/sql/2pc_on_delete_rows_transaction.sql    1 Jan 1970 00:00:00 -0000
@@ -0,0 +1,7 @@
+-- Temp table with ON DELETE ROWS option (transaction scope)
+begin;
+create temp table foo(x int) on commit delete rows;
+insert into foo values(1);
+prepare transaction 'onCommitDeleteRowsTempTableShouldSucceed';
+commit prepared 'onCommitDeleteRowsTempTableShouldSucceed';
+drop table foo;
Index: src/test/regress/expected/2pc_on_commit_drop.out
===================================================================
RCS file: src/test/regress/expected/2pc_on_commit_drop.out
diff -N src/test/regress/expected/2pc_on_commit_drop.out
--- /dev/null    1 Jan 1970 00:00:00 -0000
+++ src/test/regress/expected/2pc_on_commit_drop.out    1 Jan 1970 00:00:00 -0000
@@ -0,0 +1,6 @@
+-- Temp table with ON COMMIT DROP option
+begin;
+create temp table foo(x int) on commit drop;
+insert into foo values(1);
+prepare transaction 'onCommitDropTempTableShouldSucceed';
+commit prepared 'onCommitDropTempTableShouldSucceed';
Index: src/test/regress/expected/2pc_temp_table_transaction.out
===================================================================
RCS file: src/test/regress/expected/2pc_temp_table_transaction.out
diff -N src/test/regress/expected/2pc_temp_table_transaction.out
--- /dev/null    1 Jan 1970 00:00:00 -0000
+++ src/test/regress/expected/2pc_temp_table_transaction.out    1 Jan 1970 00:00:00 -0000
@@ -0,0 +1,7 @@
+-- Transaction-scope dropped temp table use case
+begin;
+create temp table foo(x int);
+insert into foo values(1);
+drop table foo;
+prepare transaction 'dropTempTableShouldSucceed';
+commit prepared 'dropTempTableShouldSucceed';
Index: src/test/regress/sql/2pc_temp_table_failure.sql
===================================================================
RCS file: src/test/regress/sql/2pc_temp_table_failure.sql
diff -N src/test/regress/sql/2pc_temp_table_failure.sql
--- /dev/null    1 Jan 1970 00:00:00 -0000
+++ src/test/regress/sql/2pc_temp_table_failure.sql    1 Jan 1970 00:00:00 -0000
@@ -0,0 +1,6 @@
+-- Existing non-empty temp table at commit time should still fail
+begin;
+create temp table foo(x int);
+insert into foo values(1);
+prepare transaction 'existingTempTableShouldFail';
+commit prepared 'existingTempTableShouldFail';
Index: src/test/regress/expected/2pc_temp_table_savepoint.out
===================================================================
RCS file: src/test/regress/expected/2pc_temp_table_savepoint.out
diff -N src/test/regress/expected/2pc_temp_table_savepoint.out
--- /dev/null    1 Jan 1970 00:00:00 -0000
+++ src/test/regress/expected/2pc_temp_table_savepoint.out    1 Jan 1970 00:00:00 -0000
@@ -0,0 +1,8 @@
+-- Rollback to savepoint test case
+BEGIN;
+SAVEPOINT sp;
+CREATE TEMP TABLE foo(bar int4);
+INSERT INTO foo VALUES (1);
+ROLLBACK TO sp;
+PREPARE TRANSACTION 'savepointTestCase_archives.postgresql.org_pgsql-hackers_2008-03_msg00017.php';
+COMMIT PREPARED 'savepointTestCase_archives.postgresql.org_pgsql-hackers_2008-03_msg00017.php';
Index: src/test/regress/sql/2pc_temp_table_transaction.sql
===================================================================
RCS file: src/test/regress/sql/2pc_temp_table_transaction.sql
diff -N src/test/regress/sql/2pc_temp_table_transaction.sql
--- /dev/null    1 Jan 1970 00:00:00 -0000
+++ src/test/regress/sql/2pc_temp_table_transaction.sql    1 Jan 1970 00:00:00 -0000
@@ -0,0 +1,7 @@
+-- Transaction-scope dropped temp table use case
+begin;
+create temp table foo(x int);
+insert into foo values(1);
+drop table foo;
+prepare transaction 'dropTempTableShouldSucceed';
+commit prepared 'dropTempTableShouldSucceed';
Index: src/test/regress/expected/2pc_temp_table_failure.out
===================================================================
RCS file: src/test/regress/expected/2pc_temp_table_failure.out
diff -N src/test/regress/expected/2pc_temp_table_failure.out
--- /dev/null    1 Jan 1970 00:00:00 -0000
+++ src/test/regress/expected/2pc_temp_table_failure.out    1 Jan 1970 00:00:00 -0000
@@ -0,0 +1,8 @@
+-- Existing non-empty temp table at commit time should still fail
+begin;
+create temp table foo(x int);
+insert into foo values(1);
+prepare transaction 'existingTempTableShouldFail';
+ERROR:  cannot PREPARE a transaction that has operated on temporary tables that are not empty at commit time
+commit prepared 'existingTempTableShouldFail';
+ERROR:  prepared transaction with identifier "existingTempTableShouldFail" does not exist
Index: src/test/regress/sql/2pc_temp_table_session.sql
===================================================================
RCS file: src/test/regress/sql/2pc_temp_table_session.sql
diff -N src/test/regress/sql/2pc_temp_table_session.sql
--- /dev/null    1 Jan 1970 00:00:00 -0000
+++ src/test/regress/sql/2pc_temp_table_session.sql    1 Jan 1970 00:00:00 -0000
@@ -0,0 +1,8 @@
+-- Session-scope temp table use case
+create temp table foo(x int);
+begin;
+insert into foo values(1);
+delete from foo;
+prepare transaction 'dropTempTableShouldSucceed';
+commit prepared 'dropTempTableShouldSucceed';
+drop table foo;
Index: src/test/regress/expected/2pc_dirty_buffer_check.out
===================================================================
RCS file: src/test/regress/expected/2pc_dirty_buffer_check.out
diff -N src/test/regress/expected/2pc_dirty_buffer_check.out
--- /dev/null    1 Jan 1970 00:00:00 -0000
+++ src/test/regress/expected/2pc_dirty_buffer_check.out    1 Jan 1970 00:00:00 -0000
@@ -0,0 +1,52 @@
+-- 2PC Dirty buffer check
+begin;
+create temp table foo(a int, b int, c int) on commit drop;
+insert into foo values(1,1,1);
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+prepare transaction 'bcd';
+commit prepared 'bcd';
+begin;
+create temp table bar(a int, b int, c int) on commit drop;
+insert into bar values(1,1,1);
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+commit;
Index: src/test/regress/sql/2pc_on_commit_drop.sql
===================================================================
RCS file: src/test/regress/sql/2pc_on_commit_drop.sql
diff -N src/test/regress/sql/2pc_on_commit_drop.sql
--- /dev/null    1 Jan 1970 00:00:00 -0000
+++ src/test/regress/sql/2pc_on_commit_drop.sql    1 Jan 1970 00:00:00 -0000
@@ -0,0 +1,6 @@
+-- Temp table with ON COMMIT DROP option
+begin;
+create temp table foo(x int) on commit drop;
+insert into foo values(1);
+prepare transaction 'onCommitDropTempTableShouldSucceed';
+commit prepared 'onCommitDropTempTableShouldSucceed';
Index: src/test/regress/sql/2pc_temp_table_savepoint.sql
===================================================================
RCS file: src/test/regress/sql/2pc_temp_table_savepoint.sql
diff -N src/test/regress/sql/2pc_temp_table_savepoint.sql
--- /dev/null    1 Jan 1970 00:00:00 -0000
+++ src/test/regress/sql/2pc_temp_table_savepoint.sql    1 Jan 1970 00:00:00 -0000
@@ -0,0 +1,8 @@
+-- Rollback to savepoint test case
+BEGIN;
+SAVEPOINT sp;
+CREATE TEMP TABLE foo(bar int4);
+INSERT INTO foo VALUES (1);
+ROLLBACK TO sp;
+PREPARE TRANSACTION 'savepointTestCase_archives.postgresql.org_pgsql-hackers_2008-03_msg00017.php';
+COMMIT PREPARED 'savepointTestCase_archives.postgresql.org_pgsql-hackers_2008-03_msg00017.php';
Index: src/test/regress/sql/2pc_temp_table_rollback.sql
===================================================================
RCS file: src/test/regress/sql/2pc_temp_table_rollback.sql
diff -N src/test/regress/sql/2pc_temp_table_rollback.sql
--- /dev/null    1 Jan 1970 00:00:00 -0000
+++ src/test/regress/sql/2pc_temp_table_rollback.sql    1 Jan 1970 00:00:00 -0000
@@ -0,0 +1,5 @@
+-- Rollback prepared
+BEGIN;
+CREATE TEMP TABLE foo(bar int4);
+PREPARE TRANSACTION 'rollbackTestCase_archives.postgresql.org_pgsql-hackers_2008-03_msg00017.php';
+ROLLBACK PREPARED 'rollbackTestCase_archives.postgresql.org_pgsql-hackers_2008-03_msg00017.php';
Index: src/test/regress/expected/2pc_on_delete_rows_session.out
===================================================================
RCS file: src/test/regress/expected/2pc_on_delete_rows_session.out
diff -N src/test/regress/expected/2pc_on_delete_rows_session.out
--- /dev/null    1 Jan 1970 00:00:00 -0000
+++ src/test/regress/expected/2pc_on_delete_rows_session.out    1 Jan 1970 00:00:00 -0000
@@ -0,0 +1,7 @@
+-- Temp table with ON DELETE ROWS option (session scope)
+create temp table foo(x int) on commit delete rows;
+begin;
+insert into foo values(1);
+prepare transaction 'onCommitDeleteRowsTempTableShouldSucceed';
+commit prepared 'onCommitDeleteRowsTempTableShouldSucceed';
+drop table foo;
Index: src/test/regress/sql/2pc_persistent_table.sql
===================================================================
RCS file: src/test/regress/sql/2pc_persistent_table.sql
diff -N src/test/regress/sql/2pc_persistent_table.sql
--- /dev/null    1 Jan 1970 00:00:00 -0000
+++ src/test/regress/sql/2pc_persistent_table.sql    1 Jan 1970 00:00:00 -0000
@@ -0,0 +1,12 @@
+-- Creation of a persistent table (not temp)
+begin;
+create table paul(x int);
+insert into paul values(1);
+prepare transaction 'persistentTableShouldSucceed';
+commit prepared 'persistentTableShouldSucceed';
+
+-- Drop of a persistent table (not temp)
+begin;
+drop table paul;
+prepare transaction 'dropPersistentTableShouldSucceed';
+commit prepared 'dropPersistentTableShouldSucceed';
Index: src/test/regress/expected/2pc_temp_table_rollback.out
===================================================================
RCS file: src/test/regress/expected/2pc_temp_table_rollback.out
diff -N src/test/regress/expected/2pc_temp_table_rollback.out
--- /dev/null    1 Jan 1970 00:00:00 -0000
+++ src/test/regress/expected/2pc_temp_table_rollback.out    1 Jan 1970 00:00:00 -0000
@@ -0,0 +1,5 @@
+-- Rollback prepared
+BEGIN;
+CREATE TEMP TABLE foo(bar int4);
+PREPARE TRANSACTION 'rollbackTestCase_archives.postgresql.org_pgsql-hackers_2008-03_msg00017.php';
+ROLLBACK PREPARED 'rollbackTestCase_archives.postgresql.org_pgsql-hackers_2008-03_msg00017.php';
Index: src/test/regress/sql/2pc_dirty_buffer_check.sql
===================================================================
RCS file: src/test/regress/sql/2pc_dirty_buffer_check.sql
diff -N src/test/regress/sql/2pc_dirty_buffer_check.sql
--- /dev/null    1 Jan 1970 00:00:00 -0000
+++ src/test/regress/sql/2pc_dirty_buffer_check.sql    1 Jan 1970 00:00:00 -0000
@@ -0,0 +1,52 @@
+-- 2PC Dirty buffer check
+begin;
+create temp table foo(a int, b int, c int) on commit drop;
+insert into foo values(1,1,1);
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+insert into foo select * from foo;
+prepare transaction 'bcd';
+commit prepared 'bcd';
+begin;
+create temp table bar(a int, b int, c int) on commit drop;
+insert into bar values(1,1,1);
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+insert into bar select * from bar;
+commit;
Index: src/test/regress/expected/2pc_persistent_table.out
===================================================================
RCS file: src/test/regress/expected/2pc_persistent_table.out
diff -N src/test/regress/expected/2pc_persistent_table.out
--- /dev/null    1 Jan 1970 00:00:00 -0000
+++ src/test/regress/expected/2pc_persistent_table.out    1 Jan 1970 00:00:00 -0000
@@ -0,0 +1,11 @@
+-- Creation of a persistent table (not temp)
+begin;
+create table paul(x int);
+insert into paul values(1);
+prepare transaction 'persistentTableShouldSucceed';
+commit prepared 'persistentTableShouldSucceed';
+-- Drop of a persistent table (not temp)
+begin;
+drop table paul;
+prepare transaction 'dropPersistentTableShouldSucceed';
+commit prepared 'dropPersistentTableShouldSucceed';
Index: src/test/regress/expected/2pc_temp_table_session.out
===================================================================
RCS file: src/test/regress/expected/2pc_temp_table_session.out
diff -N src/test/regress/expected/2pc_temp_table_session.out
--- /dev/null    1 Jan 1970 00:00:00 -0000
+++ src/test/regress/expected/2pc_temp_table_session.out    1 Jan 1970 00:00:00 -0000
@@ -0,0 +1,8 @@
+-- Session-scope temp table use case
+create temp table foo(x int);
+begin;
+insert into foo values(1);
+delete from foo;
+prepare transaction 'dropTempTableShouldSucceed';
+commit prepared 'dropTempTableShouldSucceed';
+drop table foo;
Index: src/test/regress/sql/2pc_on_delete_rows_session.sql
===================================================================
RCS file: src/test/regress/sql/2pc_on_delete_rows_session.sql
diff -N src/test/regress/sql/2pc_on_delete_rows_session.sql
--- /dev/null    1 Jan 1970 00:00:00 -0000
+++ src/test/regress/sql/2pc_on_delete_rows_session.sql    1 Jan 1970 00:00:00 -0000
@@ -0,0 +1,7 @@
+-- Temp table with ON DELETE ROWS option (session scope)
+create temp table foo(x int) on commit delete rows;
+begin;
+insert into foo values(1);
+prepare transaction 'onCommitDeleteRowsTempTableShouldSucceed';
+commit prepared 'onCommitDeleteRowsTempTableShouldSucceed';
+drop table foo;
Index: src/test/regress/expected/2pc_on_delete_rows_transaction.out
===================================================================
RCS file: src/test/regress/expected/2pc_on_delete_rows_transaction.out
diff -N src/test/regress/expected/2pc_on_delete_rows_transaction.out
--- /dev/null    1 Jan 1970 00:00:00 -0000
+++ src/test/regress/expected/2pc_on_delete_rows_transaction.out    1 Jan 1970 00:00:00 -0000
@@ -0,0 +1,7 @@
+-- Temp table with ON DELETE ROWS option (transaction scope)
+begin;
+create temp table foo(x int) on commit delete rows;
+insert into foo values(1);
+prepare transaction 'onCommitDeleteRowsTempTableShouldSucceed';
+commit prepared 'onCommitDeleteRowsTempTableShouldSucceed';
+drop table foo;
### Eclipse Workspace Patch 1.0
#P Postgres-HEAD
Index: src/backend/access/heap/heapam.c
===================================================================
RCS file: /root/cvsrepo/pgsql/src/backend/access/heap/heapam.c,v
retrieving revision 1.264
diff -u -r1.264 heapam.c
--- src/backend/access/heap/heapam.c    30 Sep 2008 10:52:10 -0000    1.264
+++ src/backend/access/heap/heapam.c    8 Oct 2008 01:53:44 -0000
@@ -878,7 +878,7 @@

     /* Make note that we've accessed a temporary relation */
     if (r->rd_istemp)
-        MyXactAccessedTempRel = true;
+        enlistRelationIdFor2PCChecks(relationId);

     pgstat_initstats(r);

@@ -926,7 +926,7 @@

     /* Make note that we've accessed a temporary relation */
     if (r->rd_istemp)
-        MyXactAccessedTempRel = true;
+        enlistRelationIdFor2PCChecks(relationId);

     pgstat_initstats(r);

@@ -976,7 +976,7 @@

     /* Make note that we've accessed a temporary relation */
     if (r->rd_istemp)
-        MyXactAccessedTempRel = true;
+        enlistRelationIdFor2PCChecks(relationId);

     pgstat_initstats(r);

Index: src/backend/access/transam/xact.c
===================================================================
RCS file: /root/cvsrepo/pgsql/src/backend/access/transam/xact.c,v
retrieving revision 1.265
diff -u -r1.265 xact.c
--- src/backend/access/transam/xact.c    11 Aug 2008 11:05:10 -0000    1.265
+++ src/backend/access/transam/xact.c    8 Oct 2008 01:53:44 -0000
@@ -47,6 +47,7 @@
 #include "utils/memutils.h"
 #include "utils/relcache.h"
 #include "utils/snapmgr.h"
+#include "utils/tqual.h"
 #include "utils/xml.h"
 #include "pg_trace.h"

@@ -65,13 +66,6 @@
 int            CommitDelay = 0;    /* precommit delay in microseconds */
 int            CommitSiblings = 5; /* # concurrent xacts needed to sleep */

-/*
- * MyXactAccessedTempRel is set when a temporary relation is accessed.
- * We don't allow PREPARE TRANSACTION in that case.  (This is global
- * so that it can be set from heapam.c.)
- */
-bool        MyXactAccessedTempRel = false;
-

 /*
  *    transaction states - transaction state from server perspective
@@ -209,6 +203,9 @@
  */
 static MemoryContext TransactionAbortContext = NULL;

+/* Hash table containing Oids of accessed temporary relations */
+HTAB    *accessedTempRel;
+
 /*
  * List of add-on start- and end-of-xact callbacks
  */
@@ -1511,7 +1508,6 @@
     XactIsoLevel = DefaultXactIsoLevel;
     XactReadOnly = DefaultXactReadOnly;
     forceSyncCommit = false;
-    MyXactAccessedTempRel = false;

     /*
      * reinitialize within-transaction counters
@@ -1777,6 +1773,36 @@
     RESUME_INTERRUPTS();
 }

+/* ----------------
+ *     enlistRelationIdFor2PCChecks - enlist a relation in the list of
+ *      resources to check at PREPARE COMMIT time if we are part of
+ *      a 2PC transaction. The resource will be removed from the list
+ *      if the table is dropped before commit.
+ * ----------------
+ */
+void
+enlistRelationIdFor2PCChecks(Oid relationId)
+{
+    /*
+     * Each time a temporary relation is accessed, it is added to the
+     * accessedTempRel list. PREPARE TRANSACTION will fail if any
+     * of the accessed relation is still valid (not dropped).  (This is
+     * called from from heapam.c.)
+     */
+    if (accessedTempRel == NULL)
+    { // Allocate the list on-demand
+        HASHCTL ctl;
+
+        ctl.keysize = sizeof(Oid);
+        ctl.entrysize = sizeof(Oid);
+        accessedTempRel = hash_create("accessed temp tables", 4, &ctl,
+                HASH_ELEM);
+    }
+
+    // Add to the hash list if missing
+    Oid *tid = hash_search(accessedTempRel, &relationId, HASH_ENTER, NULL);
+    *tid = relationId;
+}

 /*
  *    PrepareTransaction
@@ -1853,14 +1879,45 @@
      * We must check this after executing any ON COMMIT actions, because
      * they might still access a temp relation.
      *
-     * XXX In principle this could be relaxed to allow some useful special
-     * cases, such as a temp table created and dropped all within the
-     * transaction.  That seems to require much more bookkeeping though.
+     * We only allow to proceed further if the accessed temp tables have
+     * been dropped before PREPARE COMMIT.
      */
-    if (MyXactAccessedTempRel)
-        ereport(ERROR,
-                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-                 errmsg("cannot PREPARE a transaction that has operated on temporary tables")));
+    if (accessedTempRel != NULL)
+    {
+        HASH_SEQ_STATUS    status;
+        Oid*            tempTableOid;
+
+        /* Prevent further updates to the list as recommended in hash_seq_init doc. */
+        hash_freeze(accessedTempRel);
+        hash_seq_init(&status, accessedTempRel);
+        while ((tempTableOid = (Oid *) hash_seq_search(&status)) != NULL)
+        { /* Check all accessed temp tables. If the table has been dropped,
+           * try_relation_open will fail and we can safely continue. */
+            Relation tempTable = try_relation_open(*tempTableOid, NoLock);
+            if (tempTable != NULL)
+            { /* We have an open temp table at PREPARE COMMIT time. We
+               * will only accept empty temp tables and throw an error
+               * in other cases. */
+                HeapScanDesc scan;
+                HeapTuple tuple;
+                scan = heap_beginscan(tempTable, SnapshotNow, 0, NULL);
+                if ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
+                {
+                    hash_seq_term(&status);
+                    hash_destroy(accessedTempRel);
+                    accessedTempRel = NULL;
+                    ereport(ERROR,
+                            (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+                                    errmsg("cannot PREPARE a transaction that has operated on temporary tables that
arenot empty at commit time"))); 
+                }
+                heap_endscan(scan);
+                relation_close(tempTable, NoLock);
+            }
+        }
+        hash_seq_term(&status);
+        hash_destroy(accessedTempRel);
+        accessedTempRel = NULL;
+    }

     /* Prevent cancel/die interrupt while cleaning up */
     HOLD_INTERRUPTS();
@@ -2151,6 +2208,12 @@
         elog(FATAL, "CleanupTransaction: unexpected state %s",
              TransStateAsString(s->state));

+    if (accessedTempRel != NULL)
+    {
+        hash_destroy(accessedTempRel);
+        accessedTempRel = NULL;
+    }
+
     /*
      * do abort cleanup processing
      */
Index: src/include/access/xact.h
===================================================================
RCS file: /root/cvsrepo/pgsql/src/include/access/xact.h,v
retrieving revision 1.95
diff -u -r1.95 xact.h
--- src/include/access/xact.h    11 Aug 2008 11:05:11 -0000    1.95
+++ src/include/access/xact.h    8 Oct 2008 01:53:44 -0000
@@ -18,6 +18,7 @@
 #include "nodes/pg_list.h"
 #include "storage/relfilenode.h"
 #include "utils/timestamp.h"
+#include "postgres_ext.h"


 /*
@@ -44,8 +45,8 @@
 /* Asynchronous commits */
 extern bool XactSyncCommit;

-/* Kluge for 2PC support */
-extern bool MyXactAccessedTempRel;
+/* List of temp tables accessed during a transaction for 2PC support */
+extern void enlistRelationIdFor2PCChecks(Oid relationId);

 /*
  *    start- and end-of-transaction callbacks for dynamically loaded modules