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Commit360392f

Browse files
author
Amit Kapila
committed
Avoid unconditionally filling in missing values with NULL in pgoutput.
52e4f0c introduced a bug in pgoutput in which missing values in tupleswere incorrectly filled in with NULL. The problem was the use ofCreateTupleDescCopy where CreateTupleDescCopyConstr was required, as theformer drops the constraints in the tuple description (specifically, thedefault value constraint) on the floor.The bug could result in incorrectness when a table replicated via`REPLICA IDENTITY FULL` underwent a schema change that added a columnwith a default value. The problem is that in such cases updates fill NULLvalues in old tuples for missing columns for default values. Then on thesubscriber, we failed to find a matching tuple and missed updating therequired row.Author: Nikhil BeneschReviewed-by: Hou Zhijie, Amit KapilaBackpatch-through: 15Discussion:http://postgr.es/m/CAPWqQZTEpZQamYsGMn6ZDRvVywwpVPiKH6OY4KSgA+NmeqFNzA@mail.gmail.com
1 parentdc9f8a7 commit360392f

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2 files changed

+55
-2
lines changed

2 files changed

+55
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lines changed

‎src/backend/replication/pgoutput/pgoutput.c

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1136,8 +1136,8 @@ init_tuple_slot(PGOutputData *data, Relation relation,
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* Create tuple table slots. Create a copy of the TupleDesc as it needs to
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* live as long as the cache remains.
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*/
1139-
oldtupdesc=CreateTupleDescCopy(RelationGetDescr(relation));
1140-
newtupdesc=CreateTupleDescCopy(RelationGetDescr(relation));
1139+
oldtupdesc=CreateTupleDescCopyConstr(RelationGetDescr(relation));
1140+
newtupdesc=CreateTupleDescCopyConstr(RelationGetDescr(relation));
11411141

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entry->old_slot=MakeSingleTupleTableSlot(oldtupdesc,&TTSOpsHeapTuple);
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entry->new_slot=MakeSingleTupleTableSlot(newtupdesc,&TTSOpsHeapTuple);

‎src/test/subscription/t/100_bugs.pl

Lines changed: 53 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -438,4 +438,57 @@
438438
$node_publisher->stop('fast');
439439
$node_subscriber->stop('fast');
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441+
# The bug was that pgoutput was incorrectly replacing missing attributes in
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# tuples with NULL. This could result in incorrect replication with
443+
# `REPLICA IDENTITY FULL`.
444+
445+
$node_publisher->rotate_logfile();
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$node_publisher->start();
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$node_subscriber->rotate_logfile();
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$node_subscriber->start();
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# Set up a table with schema `(a int, b bool)` where the `b` attribute is
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# missing for one row due to the `ALTER TABLE ... ADD COLUMN ... DEFAULT`
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# fast path.
454+
$node_publisher->safe_psql(
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'postgres',qq(
456+
CREATE TABLE tab_default (a int);
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ALTER TABLE tab_default REPLICA IDENTITY FULL;
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INSERT INTO tab_default VALUES (1);
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ALTER TABLE tab_default ADD COLUMN b bool DEFAULT false NOT NULL;
460+
INSERT INTO tab_default VALUES (2, true);
461+
CREATE PUBLICATION pub1 FOR TABLE tab_default;
462+
));
463+
464+
# Replicate to the subscriber.
465+
$node_subscriber->safe_psql(
466+
'postgres',qq(
467+
CREATE TABLE tab_default (a int, b bool);
468+
CREATE SUBSCRIPTION sub1 CONNECTION '$publisher_connstr' PUBLICATION pub1;
469+
));
470+
471+
$node_subscriber->wait_for_subscription_sync($node_publisher,'sub1');
472+
$result =$node_subscriber->safe_psql('postgres',
473+
"SELECT a, b FROM tab_default");
474+
is($result,qq(1|f
475+
2|t),'check snapshot on subscriber');
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477+
# Update all rows in the table and ensure the rows with the missing `b`
478+
# attribute replicate correctly.
479+
$node_publisher->safe_psql('postgres',
480+
"UPDATE tab_default SET a = a + 1");
481+
$node_publisher->wait_for_catchup('sub1');
482+
483+
# When the bug is present, the `1|f` row will not be updated to `2|f` because
484+
# the publisher incorrectly fills in `NULL` for `b` and publishes an update
485+
# for `1|NULL`, which doesn't exist in the subscriber.
486+
$result =$node_subscriber->safe_psql('postgres',
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"SELECT a, b FROM tab_default");
488+
is($result,qq(2|f
489+
3|t),'check replicated update on subscriber');
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491+
$node_publisher->stop('fast');
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$node_subscriber->stop('fast');
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441494
done_testing();

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