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Commitc76d0ee

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Fix race conditions when an event trigger is added concurrently with DDL.
EventTriggerTableRewrite crashed if there were table_rewrite triggerspresent, but there had not been when the calling command started.EventTriggerDDLCommandEnd called ddl_command_end triggers if present,even if there had been no such triggers when the calling command started,which would lead to a failure in pg_event_trigger_ddl_commands.In both cases, fix by doing nothing; it's better to wait till the nextcommand when things will be properly initialized.In passing, remove an elog(DEBUG1) call that might have seemed interestingfour years ago but surely isn't today.We found this because of intermittent failures in the buildfarm. Thanksto Alvaro Herrera and Andrew Gierth for analysis.Back-patch to 9.5; some of this code exists before that, but the specifichazards we need to guard against don't.Discussion:https://postgr.es/m/5767.1523995174@sss.pgh.pa.us
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‎src/backend/commands/event_trigger.c

Lines changed: 25 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -834,6 +834,19 @@ EventTriggerDDLCommandEnd(Node *parsetree)
834834
if (!IsUnderPostmaster)
835835
return;
836836

837+
/*
838+
* Also do nothing if our state isn't set up, which it won't be if there
839+
* weren't any relevant event triggers at the start of the current DDL
840+
* command. This test might therefore seem optional, but it's important
841+
* because EventTriggerCommonSetup might find triggers that didn't exist
842+
* at the time the command started. Although this function itself
843+
* wouldn't crash, the event trigger functions would presumably call
844+
* pg_event_trigger_ddl_commands which would fail. Better to do nothing
845+
* until the next command.
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*/
847+
if (!currentEventTriggerState)
848+
return;
849+
837850
runlist=EventTriggerCommonSetup(parsetree,
838851
EVT_DDLCommandEnd,"ddl_command_end",
839852
&trigdata);
@@ -885,9 +898,10 @@ EventTriggerSQLDrop(Node *parsetree)
885898
&trigdata);
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/*
888-
* Nothing to do if run list is empty. Note thisshouldn't happen,
901+
* Nothing to do if run list is empty. Note thistypically can't happen,
889902
* because if there are no sql_drop events, then objects-to-drop wouldn't
890903
* have been collected in the first place and we would have quit above.
904+
* But it could occur if event triggers were dropped partway through.
891905
*/
892906
if (runlist==NIL)
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return;
@@ -934,8 +948,6 @@ EventTriggerTableRewrite(Node *parsetree, Oid tableOid, int reason)
934948
List*runlist;
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EventTriggerDatatrigdata;
936950

937-
elog(DEBUG1,"EventTriggerTableRewrite(%u)",tableOid);
938-
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/*
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* Event Triggers are completely disabled in standalone mode. There are
941953
* (at least) two reasons for this:
@@ -955,6 +967,16 @@ EventTriggerTableRewrite(Node *parsetree, Oid tableOid, int reason)
955967
if (!IsUnderPostmaster)
956968
return;
957969

970+
/*
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* Also do nothing if our state isn't set up, which it won't be if there
972+
* weren't any relevant event triggers at the start of the current DDL
973+
* command. This test might therefore seem optional, but it's
974+
* *necessary*, because EventTriggerCommonSetup might find triggers that
975+
* didn't exist at the time the command started.
976+
*/
977+
if (!currentEventTriggerState)
978+
return;
979+
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runlist=EventTriggerCommonSetup(parsetree,
959981
EVT_TableRewrite,
960982
"table_rewrite",

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