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Repair incorrect handling of AfterTriggerSharedData.ats_modifiedcols.
This patch fixes two distinct errors that both ultimately trace to commit 71d60e2, 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 ce5aaea, 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
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3 files changed

+117
-10
lines changed

3 files changed

+117
-10
lines changed

‎contrib/lo/expected/lo.out

Lines changed: 69 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -47,4 +47,73 @@ SELECT lo_get(43214);
4747
DELETE FROM image;
4848
SELECT lo_get(43214);
4949
ERROR: large object 43214 does not exist
50+
-- Now let's try it with an AFTER trigger
51+
DROP TRIGGER t_raster ON image;
52+
CREATE CONSTRAINT TRIGGER t_raster AFTER UPDATE OR DELETE ON image
53+
DEFERRABLE INITIALLY DEFERRED
54+
FOR EACH ROW EXECUTE PROCEDURE lo_manage(raster);
55+
SELECT lo_create(43223);
56+
lo_create
57+
-----------
58+
43223
59+
(1 row)
60+
61+
SELECT lo_create(43224);
62+
lo_create
63+
-----------
64+
43224
65+
(1 row)
66+
67+
SELECT lo_create(43225);
68+
lo_create
69+
-----------
70+
43225
71+
(1 row)
72+
73+
INSERT INTO image (title, raster) VALUES ('beautiful image', 43223);
74+
SELECT lo_get(43223);
75+
lo_get
76+
--------
77+
\x
78+
(1 row)
79+
80+
UPDATE image SET raster = 43224 WHERE title = 'beautiful image';
81+
SELECT lo_get(43223); -- gone
82+
ERROR: large object 43223 does not exist
83+
SELECT lo_get(43224);
84+
lo_get
85+
--------
86+
\x
87+
(1 row)
88+
89+
-- test updating of unrelated column
90+
UPDATE image SET title = 'beautiful picture' WHERE title = 'beautiful image';
91+
SELECT lo_get(43224);
92+
lo_get
93+
--------
94+
\x
95+
(1 row)
96+
97+
-- this case used to be buggy
98+
BEGIN;
99+
UPDATE image SET title = 'beautiful image' WHERE title = 'beautiful picture';
100+
UPDATE image SET raster = 43225 WHERE title = 'beautiful image';
101+
SELECT lo_get(43224);
102+
lo_get
103+
--------
104+
\x
105+
(1 row)
106+
107+
COMMIT;
108+
SELECT lo_get(43224); -- gone
109+
ERROR: large object 43224 does not exist
110+
SELECT lo_get(43225);
111+
lo_get
112+
--------
113+
\x
114+
(1 row)
115+
116+
DELETE FROM image;
117+
SELECT lo_get(43225); -- gone
118+
ERROR: large object 43225 does not exist
50119
DROP TABLE image;

‎contrib/lo/sql/lo.sql

Lines changed: 40 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -27,4 +27,44 @@ DELETE FROM image;
2727

2828
SELECT lo_get(43214);
2929

30+
-- Now let's try it with an AFTER trigger
31+
32+
DROP TRIGGER t_raster ON image;
33+
34+
CREATE CONSTRAINT TRIGGER t_raster AFTER UPDATE OR DELETE ON image
35+
DEFERRABLE INITIALLY DEFERRED
36+
FOR EACH ROW EXECUTE PROCEDURE lo_manage(raster);
37+
38+
SELECT lo_create(43223);
39+
SELECT lo_create(43224);
40+
SELECT lo_create(43225);
41+
42+
INSERT INTO image (title, raster) VALUES ('beautiful image', 43223);
43+
44+
SELECT lo_get(43223);
45+
46+
UPDATE image SET raster = 43224 WHERE title = 'beautiful image';
47+
48+
SELECT lo_get(43223); -- gone
49+
SELECT lo_get(43224);
50+
51+
-- test updating of unrelated column
52+
UPDATE image SET title = 'beautiful picture' WHERE title = 'beautiful image';
53+
54+
SELECT lo_get(43224);
55+
56+
-- this case used to be buggy
57+
BEGIN;
58+
UPDATE image SET title = 'beautiful image' WHERE title = 'beautiful picture';
59+
UPDATE image SET raster = 43225 WHERE title = 'beautiful image';
60+
SELECT lo_get(43224);
61+
COMMIT;
62+
63+
SELECT lo_get(43224); -- gone
64+
SELECT lo_get(43225);
65+
66+
DELETE FROM image;
67+
68+
SELECT lo_get(43225); -- gone
69+
3070
DROP TABLE image;

‎src/backend/commands/trigger.c

Lines changed: 8 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -3626,13 +3626,6 @@ afterTriggerCopyBitmap(Bitmapset *src)
36263626
if (src == NULL)
36273627
return NULL;
36283628

3629-
/* Create event context if we didn't already */
3630-
if (afterTriggers.event_cxt == NULL)
3631-
afterTriggers.event_cxt =
3632-
AllocSetContextCreate(TopTransactionContext,
3633-
"AfterTriggerEvents",
3634-
ALLOCSET_DEFAULT_SIZES);
3635-
36363629
oldcxt = MemoryContextSwitchTo(afterTriggers.event_cxt);
36373630

36383631
dst = bms_copy(src);
@@ -3734,16 +3727,21 @@ afterTriggerAddEvent(AfterTriggerEventList *events,
37343727
(char *) newshared >= chunk->endfree;
37353728
newshared--)
37363729
{
3730+
/* compare fields roughly by probability of them being different */
37373731
if (newshared->ats_tgoid == evtshared->ats_tgoid &&
3738-
newshared->ats_relid == evtshared->ats_relid &&
37393732
newshared->ats_event == evtshared->ats_event &&
3733+
newshared->ats_firing_id == 0 &&
37403734
newshared->ats_table == evtshared->ats_table &&
3741-
newshared->ats_firing_id == 0)
3735+
newshared->ats_relid == evtshared->ats_relid &&
3736+
bms_equal(newshared->ats_modifiedcols,
3737+
evtshared->ats_modifiedcols))
37423738
break;
37433739
}
37443740
if ((char *) newshared < chunk->endfree)
37453741
{
37463742
*newshared = *evtshared;
3743+
/* now we must make a suitably-long-lived copy of the bitmap */
3744+
newshared->ats_modifiedcols = afterTriggerCopyBitmap(evtshared->ats_modifiedcols);
37473745
newshared->ats_firing_id = 0; /* just to be sure */
37483746
chunk->endfree = (char *) newshared;
37493747
}
@@ -5759,7 +5757,7 @@ AfterTriggerSaveEvent(EState *estate, ResultRelInfo *relinfo,
57595757
new_shared.ats_table = transition_capture->tcs_private;
57605758
else
57615759
new_shared.ats_table = NULL;
5762-
new_shared.ats_modifiedcols = afterTriggerCopyBitmap(modifiedCols);
5760+
new_shared.ats_modifiedcols = modifiedCols;
57635761

57645762
afterTriggerAddEvent(&afterTriggers.query_stack[afterTriggers.query_depth].events,
57655763
&new_event, &new_shared);

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