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Use weaker locks when updating pg_subscription_rel

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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>
This commit is contained in:
Peter Eisentraut 2017-04-10 15:08:14 -04:00
parent c45b1d2283
commit 521fd4795e
1 changed files with 7 additions and 5 deletions
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12
src/backend/catalog/pg_subscription.c
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@ -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);
}