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Don't throw an error if a queued AFTER trigger no longer exists.
authorTom Lane <tgl@sss.pgh.pa.us>
Thu, 20 Jun 2024 18:21:36 +0000 (14:21 -0400)
committerTom Lane <tgl@sss.pgh.pa.us>
Thu, 20 Jun 2024 18:21:36 +0000 (14:21 -0400)
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

src/backend/commands/trigger.c patch | blob | blame | history
src/test/regress/expected/triggers.out patch | blob | blame | history
src/test/regress/sql/triggers.sql patch | blob | blame | history

diff --git a/src/backend/commands/trigger.c b/src/backend/commands/trigger.c
index 72b113476e5db0d9cd31978b0ef417c80e9d7b3e..a7f49a6731d514643a96f262e4fdd7fc1e6cba55 100644 (file)
--- a/src/backend/commands/trigger.c
+++ b/src/backend/commands/trigger.c
@@ -4390,8 +4390,12 @@ AfterTriggerExecute(EState *estate,
    bool        should_free_new = false;
 
    /*
-    * Locate trigger in trigdesc.
+    * Locate trigger in trigdesc.  It might not be present, and in fact the
+    * trigdesc could be NULL, if the trigger was dropped since the event was
+    * queued.  In that case, silently do nothing.
     */
+   if (trigdesc == NULL)
+       return;
    for (tgindx = 0; tgindx < trigdesc->numtriggers; tgindx++)
    {
        if (trigdesc->triggers[tgindx].tgoid == tgoid)
@@ -4401,7 +4405,7 @@ AfterTriggerExecute(EState *estate,
        }
    }
    if (LocTriggerData.tg_trigger == NULL)
-       elog(ERROR, "could not find trigger %u", tgoid);
+       return;
 
    /*
     * If doing EXPLAIN ANALYZE, start charging time to this trigger. We want
@@ -4782,6 +4786,7 @@ afterTriggerInvokeEvents(AfterTriggerEventList *events,
                    /* Catch calls with insufficient relcache refcounting */
                    Assert(!RelationHasReferenceCountZero(rel));
                    trigdesc = rInfo->ri_TrigDesc;
+                   /* caution: trigdesc could be NULL here */
                    finfo = rInfo->ri_TrigFunctions;
                    instr = rInfo->ri_TrigInstrument;
                    if (slot1 != NULL)
@@ -4797,9 +4802,6 @@ afterTriggerInvokeEvents(AfterTriggerEventList *events,
                        slot2 = MakeSingleTupleTableSlot(rel->rd_att,
                                                         &TTSOpsMinimalTuple);
                    }
-                   if (trigdesc == NULL)   /* should not happen */
-                       elog(ERROR, "relation %u has no triggers",
-                            evtshared->ats_relid);
                }
 
                /*
diff --git a/src/test/regress/expected/triggers.out b/src/test/regress/expected/triggers.out
index 4dd95e268090573e018f8753114460b795e9ef46..0d2c5daab313c8a260519342ddfe934cad905fb3 100644 (file)
--- a/src/test/regress/expected/triggers.out
+++ b/src/test/regress/expected/triggers.out
@@ -3372,6 +3372,17 @@ select * from trig_table;
 
 drop table refd_table, trig_table;
 --
+-- Test that we can drop a not-yet-fired deferred trigger
+--
+create table refd_table (id int primary key);
+create table trig_table (fk int references refd_table initially deferred);
+begin;
+insert into trig_table values (1);
+drop table refd_table cascade;
+NOTICE:  drop cascades to constraint trig_table_fk_fkey on table trig_table
+commit;
+drop table trig_table;
+--
 -- self-referential FKs are even more fun
 --
 create table self_ref (a int primary key,
diff --git a/src/test/regress/sql/triggers.sql b/src/test/regress/sql/triggers.sql
index 6c9e066397fc36c69186e5febc970a31be23e162..51610788b212abc54fdbbd7c0f074ecb70c5300a 100644 (file)
--- a/src/test/regress/sql/triggers.sql
+++ b/src/test/regress/sql/triggers.sql
@@ -2478,6 +2478,20 @@ select * from trig_table;
 
 drop table refd_table, trig_table;
 
+--
+-- Test that we can drop a not-yet-fired deferred trigger
+--
+
+create table refd_table (id int primary key);
+create table trig_table (fk int references refd_table initially deferred);
+
+begin;
+insert into trig_table values (1);
+drop table refd_table cascade;
+commit;
+
+drop table trig_table;
+
 --
 -- self-referential FKs are even more fun
 --
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