Horton

Re: BUG #18988: DROP SUBSCRIPTION locks not-yet-accessed database

Dilip Kumar <dilipbalaut@gmail.com>

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From: Dilip Kumar <dilipbalaut@gmail.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: vignesh C <vignesh21@gmail.com>, Álvaro Herrera <alvherre@kurilemu.de>, "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, "exclusion@gmail.com" <exclusion@gmail.com>, "pgsql-bugs@lists.postgresql.org" <pgsql-bugs@lists.postgresql.org>
Date: 2025-08-14T08:35:32Z
Lists: pgsql-bugs

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  1. Fix self-deadlock during DROP SUBSCRIPTION.

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On Thu, Aug 14, 2025 at 11:39 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Wed, Aug 13, 2025 at 3:00 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> >
> > I have prepared back branch patches.
> >
>
> @@ -1802,11 +1802,7 @@ DropSubscription(DropSubscriptionStmt *stmt,
> bool isTopLevel)
> ...
> - /*
> - * Lock pg_subscription with AccessExclusiveLock to ensure that the
> - * launcher doesn't restart new worker during dropping the subscription
> - */
> - rel = table_open(SubscriptionRelationId, AccessExclusiveLock);
> + rel = table_open(SubscriptionRelationId, AccessShareLock);
>
> We need to acquire RowExclusiveLock here as we are deleting the
> subscription row during this operation. See docs [1] and
> AlterSubscription() code for reference.

Yeah that's right

Attached is a top-up patch to
> fix this for HEAD. Additionally, I have edited a few comments. If you
> agree with these changes then please prepare backbranch patches
> accordingly.

Yeah this looks fine to me.  PFA patches for back branches.


-- 
Regards,
Dilip Kumar
Google