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Change the default value of max_prepared_transactions to zero, and add

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documentation warnings against setting it nonzero unless active use of
prepared transactions is intended and a suitable transaction manager has been
installed.  This should help to prevent the type of scenario we've seen
several times now where a prepared transaction is forgotten and eventually
causes severe maintenance problems (or even anti-wraparound shutdown).

The only real reason we had the default be nonzero in the first place was to
support regression testing of the feature.  To still be able to do that,
tweak pg_regress to force a nonzero value during "make check".  Since we
cannot force a nonzero value in "make installcheck", add a variant regression
test "expected" file that shows the results that will be obtained when
max_prepared_transactions is zero.

Also, extend the HINT messages for transaction wraparound warnings to mention
the possibility that old prepared transactions are causing the problem.

All per today's discussion.
This commit is contained in:
Tom Lane
2009-04-23 00:23:46 +00:00
parent bae8102f52
commit 8d4f2ecd41
10 changed files with 304 additions and 52 deletions
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4
src/backend/utils/misc/guc.c
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@ -10,7 +10,7 @@
* Written by Peter Eisentraut <peter_e@gmx.net>.
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.502 2009/04/07 23:27:34 momjian Exp $
* $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.503 2009/04/23 00:23:45 tgl Exp $
*
*--------------------------------------------------------------------
*/
@ -1504,7 +1504,7 @@ static struct config_int ConfigureNamesInt[] =
NULL
},
&max_prepared_xacts,
5, 0, INT_MAX, NULL, NULL
0, 0, INT_MAX / 4, NULL, NULL
},
#ifdef LOCK_DEBUG