On 6/20/17 19:10, Peter Eisentraut wrote:
> On 6/19/17 22:54, Masahiko Sawada wrote:
>>> It seems to me we could just take a stronger lock around
>>> RemoveSubscriptionRel(), so that workers can't write in there concurrently.
>>
>> Since we reduced the lock level of updating pg_subscription_rel by
>> commit 521fd4795e3e the same deadlock issue will appear if we just
>> take a stronger lock level.
>
> I was thinking about a more refined approach, like in the attached
> patch. It just changes the locking when in DropSubscription(), so that
> that doesn't fail if workers are doing stuff concurrently. Everything
> else stays the same.
The alternative is that we use the LockSharedObject() approach that was
already alluded to, like in the attached patch. Both approaches would
work equally fine AFAICT.
--
Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
From 10afa9807014e14596cb05d70ba302c86bf30dd3 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <pete...@gmx.net>
Date: Wed, 21 Jun 2017 22:40:22 -0400
Subject: [PATCH] WIP Add locking SetSubscriptionRelState()
---
src/backend/catalog/pg_subscription.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/src/backend/catalog/pg_subscription.c
b/src/backend/catalog/pg_subscription.c
index c69c461b62..f794d4c526 100644
--- a/src/backend/catalog/pg_subscription.c
+++ b/src/backend/catalog/pg_subscription.c
@@ -28,6 +28,8 @@
#include "nodes/makefuncs.h"
+#include "storage/lmgr.h"
+
#include "utils/array.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"
@@ -246,6 +248,8 @@ SetSubscriptionRelState(Oid subid, Oid relid, char state,
bool nulls[Natts_pg_subscription_rel];
Datum values[Natts_pg_subscription_rel];
+ LockSharedObject(SubscriptionRelationId, subid, 0, AccessExclusiveLock);
+
rel = heap_open(SubscriptionRelRelationId, RowExclusiveLock);
/* Try finding existing mapping. */
--
2.13.1
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