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Fix a deadlock during ALTER SUBSCRIPTION ... DROP PUBLICATION.

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A deadlock can occur when the DDL command and the apply worker acquire
catalog locks in different orders while dropping replication origins.

The issue is rare in PG16 and higher branches because, in most cases, the
tablesync worker performs the origin drop in those branches, and its
locking sequence does not conflict with DDL operations.

This patch ensures consistent lock acquisition to prevent such deadlocks.

As per buildfarm.

Reported-by: Alexander Lakhin <exclusion@gmail.com>
Author: Ajin Cherian <itsajin@gmail.com>
Reviewed-by: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Reviewed-by: vignesh C <vignesh21@gmail.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Backpatch-through: 14, where it was introduced
Discussion: https://postgr.es/m/bab95e12-6cc5-4ebb-80a8-3e41956aa297@gmail.com
This commit is contained in:
Amit Kapila
2025-08-01 07:23:37 +00:00
parent 22f126da6c
commit 434d2d147b
3 changed files with 55 additions and 7 deletions
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27
src/backend/replication/logical/tablesync.c
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@@ -379,6 +379,7 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
static HTAB *last_start_times = NULL;
ListCell *lc;
bool started_tx = false;
Relation rel = NULL;
Assert(!IsTransactionState());
@@ -470,7 +471,16 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
* refresh for the subscription where we remove the table
* state and its origin and by this time the origin might be
* already removed. So passing missing_ok = true.
*
* Lock the subscription and origin in the same order as we
* are doing during DDL commands to avoid deadlocks. See
* AlterSubscription_refresh.
*/
LockSharedObject(SubscriptionRelationId, MyLogicalRepWorker->subid,
0, AccessShareLock);
if (!rel)
rel = table_open(SubscriptionRelRelationId, RowExclusiveLock);
ReplicationOriginNameForTablesync(MyLogicalRepWorker->subid,
rstate->relid,
originname,
@@ -480,9 +490,9 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
/*
* Update the state to READY only after the origin cleanup.
*/
UpdateSubscriptionRelState(MyLogicalRepWorker->subid,
rstate->relid, rstate->state,
rstate->lsn);
UpdateSubscriptionRelStateEx(MyLogicalRepWorker->subid,
rstate->relid, rstate->state,
rstate->lsn, true);
}
}
else
@@ -533,7 +543,14 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
* This is required to avoid any undetected deadlocks
* due to any existing lock as deadlock detector won't
* be able to detect the waits on the latch.
*
* Also close any tables prior to the commit.
*/
if (rel)
{
table_close(rel, NoLock);
rel = NULL;
}
CommitTransactionCommand();
pgstat_report_stat(false);
}
@@ -593,6 +610,10 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
}
}
/* Close table if opened */
if (rel)
table_close(rel, NoLock);
if (started_tx)
{
CommitTransactionCommand();