From 521fd4795e3ec3d0b263b62e5eb58e1557be9c86 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter_e@gmx.net>
Date: Mon, 10 Apr 2017 15:08:14 -0400
Subject: [PATCH] Use weaker locks when updating pg_subscription_rel
The previously used ShareRowExclusiveLock, while technically probably
more correct, led to deadlocks during seemingly unrelated operations and
thus a poor experience. Use RowExclusiveLock, like for most similar
catalog operations. In some care cases, the user might see an error
from DDL commands.
Discussion: https://www.postgresql.org/message-id/flat/13592.1490851519%40sss.pgh.pa.us
Author: Petr Jelinek <petr.jelinek@2ndquadrant.com>
---
src/backend/catalog/pg_subscription.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)
diff --git a/src/backend/catalog/pg_subscription.c b/src/backend/catalog/pg_subscription.c
index e420ec14d23..f5ba9f6d13c 100644
--- a/src/backend/catalog/pg_subscription.c
+++ b/src/backend/catalog/pg_subscription.c
@@ -214,6 +214,10 @@ textarray_to_stringlist(ArrayType *textarray)
/*
* Set the state of a subscription table.
+ *
+ * The insert-or-update logic in this function is not concurrency safe so it
+ * might raise an error in rare circumstances. But if we took a stronger lock
+ * such as ShareRowExclusiveLock, we would risk more deadlocks.
*/
Oid
SetSubscriptionRelState(Oid subid, Oid relid, char state,
@@ -225,8 +229,7 @@ SetSubscriptionRelState(Oid subid, Oid relid, char state,
bool nulls[Natts_pg_subscription_rel];
Datum values[Natts_pg_subscription_rel];
- /* Prevent concurrent changes. */
- rel = heap_open(SubscriptionRelRelationId, ShareRowExclusiveLock);
+ rel = heap_open(SubscriptionRelRelationId, RowExclusiveLock);
/* Try finding existing mapping. */
tup = SearchSysCacheCopy2(SUBSCRIPTIONRELMAP,
@@ -357,8 +360,7 @@ RemoveSubscriptionRel(Oid subid, Oid relid)
HeapTuple tup;
int nkeys = 0;
- /* Prevent concurrent changes (see SetSubscriptionRelState()). */
- rel = heap_open(SubscriptionRelRelationId, ShareRowExclusiveLock);
+ rel = heap_open(SubscriptionRelRelationId, RowExclusiveLock);
if (OidIsValid(subid))
{
@@ -386,7 +388,7 @@ RemoveSubscriptionRel(Oid subid, Oid relid)
}
heap_endscan(scan);
- heap_close(rel, ShareRowExclusiveLock);
+ heap_close(rel, RowExclusiveLock);
}
--
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