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Don't throw an error if a queued AFTER trigger no longer exists.
afterTriggerInvokeEvents and AfterTriggerExecute have always treated it as an error if the trigger OID mentioned in a queued after-trigger event can't be found. However, that fails to account for the edge case where the trigger's been dropped in the current transaction since queueing the event. There seems no very good reason to disallow that case, so instead silently do nothing if the trigger OID can't be found. This does give up a little bit of bug-detection ability, but I don't recall that these error messages have ever actually revealed a bug, so it seems mostly theoretical. Alternatives such as marking pending events DONE at the time of dropping a trigger would be complicated and perhaps introduce bugs of their own. Per bug #18517 from Alexander Lakhin. Back-patch to all supported branches. Discussion: https://postgr.es/m/18517-af2d19882240902c@postgresql.org
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+32
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3 files changed

+32
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src/backend/commands/trigger.c

+7-5
Original file line numberDiff line numberDiff line change
@@ -4289,8 +4289,12 @@ AfterTriggerExecute(EState *estate,
42894289
bool should_free_new = false;
42904290

42914291
/*
4292-
* Locate trigger in trigdesc.
4292+
* Locate trigger in trigdesc. It might not be present, and in fact the
4293+
* trigdesc could be NULL, if the trigger was dropped since the event was
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* queued. In that case, silently do nothing.
42934295
*/
4296+
if (trigdesc == NULL)
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return;
42944298
for (tgindx = 0; tgindx < trigdesc->numtriggers; tgindx++)
42954299
{
42964300
if (trigdesc->triggers[tgindx].tgoid == tgoid)
@@ -4300,7 +4304,7 @@ AfterTriggerExecute(EState *estate,
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}
43014305
}
43024306
if (LocTriggerData.tg_trigger == NULL)
4303-
elog(ERROR, "could not find trigger %u", tgoid);
4307+
return;
43044308

43054309
/*
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* If doing EXPLAIN ANALYZE, start charging time to this trigger. We want
@@ -4681,6 +4685,7 @@ afterTriggerInvokeEvents(AfterTriggerEventList *events,
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/* Catch calls with insufficient relcache refcounting */
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Assert(!RelationHasReferenceCountZero(rel));
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trigdesc = rInfo->ri_TrigDesc;
4688+
/* caution: trigdesc could be NULL here */
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finfo = rInfo->ri_TrigFunctions;
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instr = rInfo->ri_TrigInstrument;
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if (slot1 != NULL)
@@ -4696,9 +4701,6 @@ afterTriggerInvokeEvents(AfterTriggerEventList *events,
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slot2 = MakeSingleTupleTableSlot(rel->rd_att,
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&TTSOpsMinimalTuple);
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}
4699-
if (trigdesc == NULL) /* should not happen */
4700-
elog(ERROR, "relation %u has no triggers",
4701-
evtshared->ats_relid);
47024704
}
47034705

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/*

src/test/regress/expected/triggers.out

+11
Original file line numberDiff line numberDiff line change
@@ -3372,6 +3372,17 @@ select * from trig_table;
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33733373
drop table refd_table, trig_table;
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--
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-- Test that we can drop a not-yet-fired deferred trigger
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--
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create table refd_table (id int primary key);
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create table trig_table (fk int references refd_table initially deferred);
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begin;
3380+
insert into trig_table values (1);
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drop table refd_table cascade;
3382+
NOTICE: drop cascades to constraint trig_table_fk_fkey on table trig_table
3383+
commit;
3384+
drop table trig_table;
3385+
--
33753386
-- self-referential FKs are even more fun
33763387
--
33773388
create table self_ref (a int primary key,

src/test/regress/sql/triggers.sql

+14
Original file line numberDiff line numberDiff line change
@@ -2478,6 +2478,20 @@ select * from trig_table;
24782478

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drop table refd_table, trig_table;
24802480

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--
2482+
-- Test that we can drop a not-yet-fired deferred trigger
2483+
--
2484+
2485+
create table refd_table (id int primary key);
2486+
create table trig_table (fk int references refd_table initially deferred);
2487+
2488+
begin;
2489+
insert into trig_table values (1);
2490+
drop table refd_table cascade;
2491+
commit;
2492+
2493+
drop table trig_table;
2494+
24812495
--
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-- self-referential FKs are even more fun
24832497
--

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