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Commit8f55b9a

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Avoid memory leakage when a series of subtransactions invoke AFTER triggers
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 contextis 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 moreper subtransaction. Per off-list example from Viatcheslav Kalininsubsequent to bug #3418 (his original bug report omitted a foreign keyconstraint needed to cause this leak).Back-patch to 8.2; prior versions were not using per-subxact contextsfor deferred triggers, so did not have this leak.
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‎src/backend/commands/trigger.c

Lines changed: 19 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* IDENTIFICATION
10-
* $PostgreSQL: pgsql/src/backend/commands/trigger.c,v 1.214 2007/03/19 23:38:29 wieck Exp $
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* $PostgreSQL: pgsql/src/backend/commands/trigger.c,v 1.215 2007/07/01 17:45:42 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -2814,6 +2814,24 @@ AfterTriggerEndSubXact(bool isCommit)
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afterTriggers->state_stack[my_level]=NULL;
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Assert(afterTriggers->query_depth==
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afterTriggers->depth_stack[my_level]);
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/*
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* It's entirely possible that the subxact created an event_cxt but
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* there is not anything left in it (because all the triggers were
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* fired at end-of-statement). If so, we should release the context
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* to prevent memory leakage in a long sequence of subtransactions.
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* We can detect whether there's anything of use in the context by
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* seeing if anything was added to the global events list since
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* subxact start. (This test doesn't catch every case where the
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* context is deletable; for instance maybe the only additions were
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* from a sub-sub-xact. But it handles the common case.)
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*/
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if (afterTriggers->cxt_stack[my_level]&&
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afterTriggers->events.tail==afterTriggers->events_stack[my_level].tail)
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{
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MemoryContextDelete(afterTriggers->cxt_stack[my_level]);
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/* avoid double delete if abort later */
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afterTriggers->cxt_stack[my_level]=NULL;
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}
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}
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else
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{

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