From ea68ea6320ff84f55cf30dff1af662fc0bf5dafa Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Wed, 22 Jan 2025 11:58:20 -0500 Subject: [PATCH] Repair incorrect handling of AfterTriggerSharedData.ats_modifiedcols. This patch fixes two distinct errors that both ultimately trace to commit 71d60e2aa, which added the ats_modifiedcols field. The more severe error is that ats_modifiedcols wasn't accounted for in afterTriggerAddEvent's scanning loop that looks for a pre-existing duplicate AfterTriggerSharedData. Thus, a new event could be incorrectly matched to an AfterTriggerSharedData that has a different value of ats_modifiedcols, resulting in the wrong tg_updatedcols bitmap getting passed to the trigger whenever it finally gets fired. We'd not noticed because (a) few triggers consult tg_updatedcols, and (b) we had no tests exercising a case where such a trigger was called as an AFTER trigger. In the test case added by this commit, contrib/lo's trigger fails to remove a large object when expected because (without this fix) it thinks the LO OID column hasn't changed. The other problem was introduced by commit ce5aaea8c, which copied the modified-columns bitmap into trigger-related storage. It made a copy for every trigger event, whereas what we really want is to make a new copy only when we make a new AfterTriggerSharedData entry. (We could imagine adding extra logic to reduce the number of bitmap copies still more, but it doesn't look worthwhile at the moment.) In a simple test of an UPDATE of 10000000 rows with a single AFTER trigger, this thinko roughly tripled the amount of memory consumed by the pending-triggers data structures, from 160446744 to 480443440 bytes. Fixing the first problem requires introducing a bms_equal() call into afterTriggerAddEvent's scanning loop, which is slightly annoying from a speed perspective. However, getting rid of the excessive bms_copy() calls from the second problem balances that out; overall speed of trigger operations is the same or slightly better, in my tests. Discussion: https://postgr.es/m/3496294.1737501591@sss.pgh.pa.us Backpatch-through: 13 --- contrib/lo/expected/lo.out | 69 ++++++++++++++++++++++++++++++++++ contrib/lo/sql/lo.sql | 41 ++++++++++++++++++++ src/backend/commands/trigger.c | 18 ++++----- 3 files changed, 118 insertions(+), 10 deletions(-) diff --git a/contrib/lo/expected/lo.out b/contrib/lo/expected/lo.out index 65798205a5a..2c9c07f7830 100644 --- a/contrib/lo/expected/lo.out +++ b/contrib/lo/expected/lo.out @@ -47,6 +47,75 @@ SELECT lo_get(43214); DELETE FROM image; SELECT lo_get(43214); ERROR: large object 43214 does not exist +-- Now let's try it with an AFTER trigger +DROP TRIGGER t_raster ON image; +CREATE CONSTRAINT TRIGGER t_raster AFTER UPDATE OR DELETE ON image + DEFERRABLE INITIALLY DEFERRED + FOR EACH ROW EXECUTE PROCEDURE lo_manage(raster); +SELECT lo_create(43223); + lo_create +----------- + 43223 +(1 row) + +SELECT lo_create(43224); + lo_create +----------- + 43224 +(1 row) + +SELECT lo_create(43225); + lo_create +----------- + 43225 +(1 row) + +INSERT INTO image (title, raster) VALUES ('beautiful image', 43223); +SELECT lo_get(43223); + lo_get +-------- + \x +(1 row) + +UPDATE image SET raster = 43224 WHERE title = 'beautiful image'; +SELECT lo_get(43223); -- gone +ERROR: large object 43223 does not exist +SELECT lo_get(43224); + lo_get +-------- + \x +(1 row) + +-- test updating of unrelated column +UPDATE image SET title = 'beautiful picture' WHERE title = 'beautiful image'; +SELECT lo_get(43224); + lo_get +-------- + \x +(1 row) + +-- this case used to be buggy +BEGIN; +UPDATE image SET title = 'beautiful image' WHERE title = 'beautiful picture'; +UPDATE image SET raster = 43225 WHERE title = 'beautiful image'; +SELECT lo_get(43224); + lo_get +-------- + \x +(1 row) + +COMMIT; +SELECT lo_get(43224); -- gone +ERROR: large object 43224 does not exist +SELECT lo_get(43225); + lo_get +-------- + \x +(1 row) + +DELETE FROM image; +SELECT lo_get(43225); -- gone +ERROR: large object 43225 does not exist SELECT lo_oid(1::lo); lo_oid -------- diff --git a/contrib/lo/sql/lo.sql b/contrib/lo/sql/lo.sql index ca36cdb3098..d1a9d7cf255 100644 --- a/contrib/lo/sql/lo.sql +++ b/contrib/lo/sql/lo.sql @@ -27,6 +27,47 @@ DELETE FROM image; SELECT lo_get(43214); +-- Now let's try it with an AFTER trigger + +DROP TRIGGER t_raster ON image; + +CREATE CONSTRAINT TRIGGER t_raster AFTER UPDATE OR DELETE ON image + DEFERRABLE INITIALLY DEFERRED + FOR EACH ROW EXECUTE PROCEDURE lo_manage(raster); + +SELECT lo_create(43223); +SELECT lo_create(43224); +SELECT lo_create(43225); + +INSERT INTO image (title, raster) VALUES ('beautiful image', 43223); + +SELECT lo_get(43223); + +UPDATE image SET raster = 43224 WHERE title = 'beautiful image'; + +SELECT lo_get(43223); -- gone +SELECT lo_get(43224); + +-- test updating of unrelated column +UPDATE image SET title = 'beautiful picture' WHERE title = 'beautiful image'; + +SELECT lo_get(43224); + +-- this case used to be buggy +BEGIN; +UPDATE image SET title = 'beautiful image' WHERE title = 'beautiful picture'; +UPDATE image SET raster = 43225 WHERE title = 'beautiful image'; +SELECT lo_get(43224); +COMMIT; + +SELECT lo_get(43224); -- gone +SELECT lo_get(43225); + +DELETE FROM image; + +SELECT lo_get(43225); -- gone + + SELECT lo_oid(1::lo); DROP TABLE image; diff --git a/src/backend/commands/trigger.c b/src/backend/commands/trigger.c index acf3e4a3f1f..1fa63ab7d0f 100644 --- a/src/backend/commands/trigger.c +++ b/src/backend/commands/trigger.c @@ -4006,13 +4006,6 @@ afterTriggerCopyBitmap(Bitmapset *src) if (src == NULL) return NULL; - /* Create event context if we didn't already */ - if (afterTriggers.event_cxt == NULL) - afterTriggers.event_cxt = - AllocSetContextCreate(TopTransactionContext, - "AfterTriggerEvents", - ALLOCSET_DEFAULT_SIZES); - oldcxt = MemoryContextSwitchTo(afterTriggers.event_cxt); dst = bms_copy(src); @@ -4117,16 +4110,21 @@ afterTriggerAddEvent(AfterTriggerEventList *events, (char *) newshared >= chunk->endfree; newshared--) { + /* compare fields roughly by probability of them being different */ if (newshared->ats_tgoid == evtshared->ats_tgoid && - newshared->ats_relid == evtshared->ats_relid && newshared->ats_event == evtshared->ats_event && + newshared->ats_firing_id == 0 && newshared->ats_table == evtshared->ats_table && - newshared->ats_firing_id == 0) + newshared->ats_relid == evtshared->ats_relid && + bms_equal(newshared->ats_modifiedcols, + evtshared->ats_modifiedcols)) break; } if ((char *) newshared < chunk->endfree) { *newshared = *evtshared; + /* now we must make a suitably-long-lived copy of the bitmap */ + newshared->ats_modifiedcols = afterTriggerCopyBitmap(evtshared->ats_modifiedcols); newshared->ats_firing_id = 0; /* just to be sure */ chunk->endfree = (char *) newshared; } @@ -6437,7 +6435,7 @@ AfterTriggerSaveEvent(EState *estate, ResultRelInfo *relinfo, new_shared.ats_table = transition_capture->tcs_private; else new_shared.ats_table = NULL; - new_shared.ats_modifiedcols = afterTriggerCopyBitmap(modifiedCols); + new_shared.ats_modifiedcols = modifiedCols; afterTriggerAddEvent(&afterTriggers.query_stack[afterTriggers.query_depth].events, &new_event, &new_shared);