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Avoid memory leakage when a series of subtransactions invoke AFTER triggers

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that are fired at end-of-statement (as is the normal case for foreign keys,
for example).  In this situation the per-subxact deferred trigger context
is always empty when subtransaction exit is reached; so we could free it,
but were not doing so, leading to an intratransaction leak of 8K or more
per subtransaction.  Per off-list example from Viatcheslav Kalinin
subsequent to bug #3418 (his original bug report omitted a foreign key
constraint needed to cause this leak).

Back-patch to 8.2; prior versions were not using per-subxact contexts
for deferred triggers, so did not have this leak.
This commit is contained in:
Tom Lane 2007-07-01 17:45:49 +00:00
parent f6eafabc6e
commit b60765944d
1 changed files with 19 additions and 1 deletions
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20
src/backend/commands/trigger.c
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@ -7,7 +7,7 @@
* Portions Copyright (c) 1994, Regents of the University of California * Portions Copyright (c) 1994, Regents of the University of California
* *
* IDENTIFICATION * IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/commands/trigger.c,v 1.210.2.1 2007/01/25 04:17:56 momjian Exp $ * $PostgreSQL: pgsql/src/backend/commands/trigger.c,v 1.210.2.2 2007/07/01 17:45:49 tgl Exp $
* *
*------------------------------------------------------------------------- *-------------------------------------------------------------------------
*/ */
@ -2766,6 +2766,24 @@ AfterTriggerEndSubXact(bool isCommit)
afterTriggers->state_stack[my_level] = NULL; afterTriggers->state_stack[my_level] = NULL;
Assert(afterTriggers->query_depth == Assert(afterTriggers->query_depth ==
afterTriggers->depth_stack[my_level]); afterTriggers->depth_stack[my_level]);
/*
* It's entirely possible that the subxact created an event_cxt but
* there is not anything left in it (because all the triggers were
* fired at end-of-statement). If so, we should release the context
* to prevent memory leakage in a long sequence of subtransactions.
* We can detect whether there's anything of use in the context by
* seeing if anything was added to the global events list since
* subxact start. (This test doesn't catch every case where the
* context is deletable; for instance maybe the only additions were
* from a sub-sub-xact. But it handles the common case.)
*/
if (afterTriggers->cxt_stack[my_level] &&
afterTriggers->events.tail == afterTriggers->events_stack[my_level].tail)
{
MemoryContextDelete(afterTriggers->cxt_stack[my_level]);
/* avoid double delete if abort later */
afterTriggers->cxt_stack[my_level] = NULL;
}
} }
else else
{ {