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Commit5d3fcb5

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Fix bogus tuple-slot management in logical replication UPDATE handling.
slot_modify_cstrings seriously abused the TupleTableSlot API by relyingon a slot's underlying data to stay valid across ExecClearTuple. Sincethis abuse was also quite undocumented, it's little surprise that thecase got broken during the v12 slot rewrites. As reported in bug #16129from Ondřej Jirman, this could lead to crashes or data corruption whena logical replication subscriber processes a row update. Problems wouldonly arise if the subscriber's table contained columns of pass-by-reftypes that were not being copied from the publisher.Fix by explicitly copying the datum/isnull arrays from the source slotthat the old row was in already. This ends up being about the samething that happened pre-v12, but hopefully in a less opaque andfragile way.We might've caught the problem sooner if there were any test casesdealing with updates involving non-replicated or dropped columns.Now there are.Back-patch to v10 where this code came in. Even though the failuredoes not manifest before v12, IMO this code is too fragile to leaveas-is. In any case we certainly want the additional test coverage.Patch by me; thanks to Tomas Vondra for initial investigation.Discussion:https://postgr.es/m/16129-a0c0f48e71741e5f@postgresql.org
1 parentb9f3d7a commit5d3fcb5

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2 files changed

+72
-17
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2 files changed

+72
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lines changed

‎src/backend/replication/logical/worker.c

Lines changed: 24 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -377,24 +377,39 @@ slot_store_cstrings(TupleTableSlot *slot, LogicalRepRelMapEntry *rel,
377377
}
378378

379379
/*
380-
*Modify slot with user data provided as C strings.
380+
*Replace selected columns with user data provided as C strings.
381381
* This is somewhat similar to heap_modify_tuple but also calls the type
382-
* input function on the user data as the input is the text representation
383-
* of the types.
382+
* input functions on the user data.
383+
* "slot" is filled with a copy of the tuple in "srcslot", with
384+
* columns selected by the "replaces" array replaced with data values
385+
* from "values".
386+
* Caution: unreplaced pass-by-ref columns in "slot" will point into the
387+
* storage for "srcslot". This is OK for current usage, but someday we may
388+
* need to materialize "slot" at the end to make it independent of "srcslot".
384389
*/
385390
staticvoid
386-
slot_modify_cstrings(TupleTableSlot*slot,LogicalRepRelMapEntry*rel,
391+
slot_modify_cstrings(TupleTableSlot*slot,TupleTableSlot*srcslot,
392+
LogicalRepRelMapEntry*rel,
387393
char**values,bool*replaces)
388394
{
389395
intnatts=slot->tts_tupleDescriptor->natts;
390396
inti;
391397
SlotErrCallbackArgerrarg;
392398
ErrorContextCallbackerrcallback;
393399

394-
slot_getallattrs(slot);
400+
/* We'll fill "slot" with a virtual tuple, so we must start with ... */
395401
ExecClearTuple(slot);
396402

397-
/* Push callback + info on the error context stack */
403+
/*
404+
* Copy all the column data from srcslot, so that we'll have valid values
405+
* for unreplaced columns.
406+
*/
407+
Assert(natts==srcslot->tts_tupleDescriptor->natts);
408+
slot_getallattrs(srcslot);
409+
memcpy(slot->tts_values,srcslot->tts_values,natts*sizeof(Datum));
410+
memcpy(slot->tts_isnull,srcslot->tts_isnull,natts*sizeof(bool));
411+
412+
/* For error reporting, push callback + info on the error context stack */
398413
errarg.rel=rel;
399414
errarg.local_attnum=-1;
400415
errarg.remote_attnum=-1;
@@ -442,6 +457,7 @@ slot_modify_cstrings(TupleTableSlot *slot, LogicalRepRelMapEntry *rel,
442457
/* Pop the error context stack */
443458
error_context_stack=errcallback.previous;
444459

460+
/* And finally, declare that "slot" contains a valid virtual tuple */
445461
ExecStoreVirtualTuple(slot);
446462
}
447463

@@ -752,8 +768,8 @@ apply_handle_update(StringInfo s)
752768
{
753769
/* Process and store remote tuple in the slot */
754770
oldctx=MemoryContextSwitchTo(GetPerTupleMemoryContext(estate));
755-
ExecStoreTuple(localslot->tts_tuple,remoteslot,InvalidBuffer, false);
756-
slot_modify_cstrings(remoteslot,rel,newtup.values,newtup.changed);
771+
slot_modify_cstrings(remoteslot,localslot,rel,
772+
newtup.values,newtup.changed);
757773
MemoryContextSwitchTo(oldctx);
758774

759775
EvalPlanQualSetSlot(&epqstate,remoteslot);

‎src/test/subscription/t/001_rep_changes.pl

Lines changed: 48 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -3,7 +3,7 @@
33
use warnings;
44
use PostgresNode;
55
use TestLib;
6-
use Test::Moretests=>16;
6+
use Test::Moretests=>19;
77

88
# Initialize publisher node
99
my$node_publisher = get_new_node('publisher');
@@ -28,9 +28,9 @@
2828
$node_publisher->safe_psql('postgres',
2929
"CREATE TABLE tab_rep (a int primary key)");
3030
$node_publisher->safe_psql('postgres',
31-
"CREATE TABLE tab_mixed (a int primary key, b text)");
31+
"CREATE TABLE tab_mixed (a int primary key, b text, c numeric)");
3232
$node_publisher->safe_psql('postgres',
33-
"INSERT INTO tab_mixed (a, b) VALUES (1, 'foo')");
33+
"INSERT INTO tab_mixed (a, b, c) VALUES (1, 'foo', 1.1)");
3434

3535
# Setup structure on subscriber
3636
$node_subscriber->safe_psql('postgres',"CREATE TABLE tab_notrep (a int)");
@@ -42,7 +42,8 @@
4242

4343
# different column count and order than on publisher
4444
$node_subscriber->safe_psql('postgres',
45-
"CREATE TABLE tab_mixed (c text, b text, a int primary key)");
45+
"CREATE TABLE tab_mixed (d text default 'local', c numeric, b text, a int primary key)"
46+
);
4647

4748
# Setup logical replication
4849
my$publisher_connstr =$node_publisher->connstr .' dbname=postgres';
@@ -91,7 +92,7 @@
9192
$node_publisher->safe_psql('postgres',"UPDATE tab_rep SET a = -a");
9293

9394
$node_publisher->safe_psql('postgres',
94-
"INSERT INTO tab_mixed VALUES (2, 'bar')");
95+
"INSERT INTO tab_mixed VALUES (2, 'bar', 2.2)");
9596

9697
$node_publisher->poll_query_until('postgres',$caughtup_query)
9798
ordie"Timed out while waiting for subscriber to catch up";
@@ -104,10 +105,9 @@
104105
"SELECT count(*), min(a), max(a) FROM tab_rep");
105106
is($result,qq(20|-20|-1),'check replicated changes on subscriber');
106107

107-
$result =
108-
$node_subscriber->safe_psql('postgres',"SELECT c, b, a FROM tab_mixed");
109-
is($result,qq(|foo|1
110-
|bar|2),'check replicated changes with different column order');
108+
$result =$node_subscriber->safe_psql('postgres',"SELECT * FROM tab_mixed");
109+
is($result,qq(local|1.1|foo|1
110+
local|2.2|bar|2),'check replicated changes with different column order');
111111

112112
# insert some duplicate rows
113113
$node_publisher->safe_psql('postgres',
@@ -126,11 +126,14 @@
126126
"ALTER TABLE tab_ins REPLICA IDENTITY FULL");
127127
$node_subscriber->safe_psql('postgres',
128128
"ALTER TABLE tab_ins REPLICA IDENTITY FULL");
129+
# tab_mixed can use DEFAULT, since it has a primary key
129130

130131
# and do the updates
131132
$node_publisher->safe_psql('postgres',"UPDATE tab_full SET a = a * a");
132133
$node_publisher->safe_psql('postgres',
133134
"UPDATE tab_full2 SET x = 'bb' WHERE x = 'b'");
135+
$node_publisher->safe_psql('postgres',
136+
"UPDATE tab_mixed SET b = 'baz' WHERE a = 1");
134137

135138
# Wait for subscription to catch up
136139
$node_publisher->poll_query_until('postgres',$caughtup_query)
@@ -148,6 +151,42 @@
148151
bb),
149152
'update works with REPLICA IDENTITY FULL and text datums');
150153

154+
$result =$node_subscriber->safe_psql('postgres',
155+
"SELECT * FROM tab_mixed ORDER BY a");
156+
is($result,qq(local|1.1|baz|1
157+
local|2.2|bar|2),
158+
'update works with different column order and subscriber local values');
159+
160+
# check behavior with dropped columns
161+
162+
$node_publisher->safe_psql('postgres',"ALTER TABLE tab_mixed DROP COLUMN b");
163+
$node_publisher->safe_psql('postgres',
164+
"UPDATE tab_mixed SET c = 11.11 WHERE a = 1");
165+
166+
$node_publisher->poll_query_until('postgres',$caughtup_query)
167+
ordie"Timed out while waiting for subscriber to catch up";
168+
169+
$result =$node_subscriber->safe_psql('postgres',
170+
"SELECT * FROM tab_mixed ORDER BY a");
171+
is($result,qq(local|11.11|baz|1
172+
local|2.2|bar|2),
173+
'update works with dropped publisher column');
174+
175+
$node_subscriber->safe_psql('postgres',
176+
"ALTER TABLE tab_mixed DROP COLUMN d");
177+
178+
$node_publisher->safe_psql('postgres',
179+
"UPDATE tab_mixed SET c = 22.22 WHERE a = 2");
180+
181+
$node_publisher->poll_query_until('postgres',$caughtup_query)
182+
ordie"Timed out while waiting for subscriber to catch up";
183+
184+
$result =$node_subscriber->safe_psql('postgres',
185+
"SELECT * FROM tab_mixed ORDER BY a");
186+
is($result,qq(11.11|baz|1
187+
22.22|bar|2),
188+
'update works with dropped subscriber column');
189+
151190
# check that change of connection string and/or publication list causes
152191
# restart of subscription workers. Not all of these are registered as tests
153192
# as we need to poll for a change but the test suite will fail none the less

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