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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/[email protected] Backpatch-through: 13
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+118
-10
lines changed

3 files changed

+118
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lines changed

‎contrib/lo/expected/lo.out‎

Lines changed: 69 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -47,6 +47,75 @@ 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+
--------
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\x
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(1 row)
106+
107+
COMMIT;
108+
SELECT lo_get(43224); -- gone
109+
ERROR: large object 43224 does not exist
110+
SELECT lo_get(43225);
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lo_get
112+
--------
113+
\x
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(1 row)
115+
116+
DELETE FROM image;
117+
SELECT lo_get(43225); -- gone
118+
ERROR: large object 43225 does not exist
50119
SELECT lo_oid(1::lo);
51120
lo_oid
52121
--------

‎contrib/lo/sql/lo.sql‎

Lines changed: 41 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -27,6 +27,47 @@ 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;
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SELECT lo_get(43224); -- gone
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SELECT lo_get(43225);
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66+
DELETE FROM image;
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68+
SELECT lo_get(43225); -- gone
69+
70+
3071
SELECT lo_oid(1::lo);
3172

3273
DROP TABLE image;

‎src/backend/commands/trigger.c‎

Lines changed: 8 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -4006,13 +4006,6 @@ afterTriggerCopyBitmap(Bitmapset *src)
40064006
if (src == NULL)
40074007
return NULL;
40084008

4009-
/* Create event context if we didn't already */
4010-
if (afterTriggers.event_cxt == NULL)
4011-
afterTriggers.event_cxt =
4012-
AllocSetContextCreate(TopTransactionContext,
4013-
"AfterTriggerEvents",
4014-
ALLOCSET_DEFAULT_SIZES);
4015-
40164009
oldcxt = MemoryContextSwitchTo(afterTriggers.event_cxt);
40174010

40184011
dst = bms_copy(src);
@@ -4117,16 +4110,21 @@ afterTriggerAddEvent(AfterTriggerEventList *events,
41174110
(char *) newshared >= chunk->endfree;
41184111
newshared--)
41194112
{
4113+
/* compare fields roughly by probability of them being different */
41204114
if (newshared->ats_tgoid == evtshared->ats_tgoid &&
4121-
newshared->ats_relid == evtshared->ats_relid &&
41224115
newshared->ats_event == evtshared->ats_event &&
4116+
newshared->ats_firing_id == 0 &&
41234117
newshared->ats_table == evtshared->ats_table &&
4124-
newshared->ats_firing_id == 0)
4118+
newshared->ats_relid == evtshared->ats_relid &&
4119+
bms_equal(newshared->ats_modifiedcols,
4120+
evtshared->ats_modifiedcols))
41254121
break;
41264122
}
41274123
if ((char *) newshared < chunk->endfree)
41284124
{
41294125
*newshared = *evtshared;
4126+
/* now we must make a suitably-long-lived copy of the bitmap */
4127+
newshared->ats_modifiedcols = afterTriggerCopyBitmap(evtshared->ats_modifiedcols);
41304128
newshared->ats_firing_id = 0; /* just to be sure */
41314129
chunk->endfree = (char *) newshared;
41324130
}
@@ -6437,7 +6435,7 @@ AfterTriggerSaveEvent(EState *estate, ResultRelInfo *relinfo,
64376435
new_shared.ats_table = transition_capture->tcs_private;
64386436
else
64396437
new_shared.ats_table = NULL;
6440-
new_shared.ats_modifiedcols = afterTriggerCopyBitmap(modifiedCols);
6438+
new_shared.ats_modifiedcols = modifiedCols;
64416439

64426440
afterTriggerAddEvent(&afterTriggers.query_stack[afterTriggers.query_depth].events,
64436441
&new_event, &new_shared);

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