Horton

Re: 024_add_drop_pub.pl might fail due to deadlock

Ajin Cherian <itsajin@gmail.com>

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From: Ajin Cherian <itsajin@gmail.com>
To: Alexander Lakhin <exclusion@gmail.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2025-07-14T09:59:52Z
Lists: pgsql-hackers

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On Tue, Jul 8, 2025 at 8:41 PM Ajin Cherian <itsajin@gmail.com> wrote:

> Proposed fix:
> In process_syncing_tables_for_apply(), acquire an AccessExclusiveLock
> on SubscriptionRelRelationId before acquiring the lock on
> ReplicationOriginRelationId.
>
> Patch with fix attached.
> I'll continue investigating whether this issue also affects HEAD.

While debugging this further, I found that there is another lock taken
prior to this in AlterSubscription(),
    /* Lock the subscription so nobody else can do anything with it. */
    LockSharedObject(SubscriptionRelationId, subid, 0, AccessExclusiveLock);

Since this is the first lock taken while altering subscription, that
should also be taken first by the tablesync worker to avoid deadlock.
So, attaching a modified patch.

regards,
Ajin Cherian
Fujitsu Australia

Commits

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