postgres.git / summary / log / commit / refs
commit ea68ea6320ff84f55cf30dff1af662fc0bf5dafa
Author: Tom Lane <tgl@sss.pgh.pa.us>
Date: Wed Jan 22 16:58:20 2025 +0000
First released in: 18.0, 13.19, 14.16, 15.11, 16.7, 17.3
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);
[parent: 991974bb4888]