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

diff --git a/src/backend/commands/trigger.c b/src/backend/commands/trigger.c
index 49048c7e7df4206d5512fc800d728fc41f8cf6eb..72dce883524fe7d4ea4e85051d8f3360ad2ef996 100644 (file)
--- a/src/backend/commands/trigger.c
+++ b/src/backend/commands/trigger.c
@@ -3900,8 +3900,12 @@ 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)
@@ -3911,7 +3915,7 @@ 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
@@ -4235,6 +4239,7 @@ 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)
@@ -4250,9 +4255,6 @@ 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 b559479f470efb7ff75ddaefe0e543b0275af428..0e027decbb465b4ce9c748f21ff69246bb2cdc3f 100644 (file)
--- a/src/test/regress/expected/triggers.out
+++ b/src/test/regress/expected/triggers.out
@@ -3286,6 +3286,17 @@ 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 b18faf0d5a2937ad4430d72170de1fe93abbc6c0..605d5cf05eed9a7db1753253266f319d113779fe 100644 (file)
--- a/src/test/regress/sql/triggers.sql
+++ b/src/test/regress/sql/triggers.sql
@@ -2406,6 +2406,20 @@ 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
 --