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Re: Assertion failure in SnapBuildInitialSnapshot()

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>
Cc: Masahiko Sawada <sawada.mshk@gmail.com>, Andres Freund <andres@anarazel.de>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Thomas Munro <thomas.munro@gmail.com>
Date: 2023-01-30T11:29:48Z
Lists: pgsql-hackers 
On Fri, Jan 27, 2023 at 4:31 PM Hayato Kuroda (Fujitsu)
<kuroda.hayato@fujitsu.com> wrote:
>
> Thank you for making the patch! I'm still considering whether this approach is
> correct, but I can put a comment to your patch anyway.
>
> ```
> -       Assert(!already_locked || LWLockHeldByMe(ProcArrayLock));
> -
> -       if (!already_locked)
> -               LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
> +       Assert(LWLockHeldByMe(ProcArrayLock));
> ```
>
> In this function, we regard that the ProcArrayLock has been already acquired as
> exclusive mode and modify data. I think LWLockHeldByMeInMode() should be used
> instead of LWLockHeldByMe().
>

Right, this is even evident from the comments atop
ReplicationSlotsComputeRequiredXmin("If already_locked is true,
ProcArrayLock has already been acquired exclusively.". But, I am not
sure if it is a good idea to remove 'already_locked' parameter,
especially in back branches as this is an exposed API.

-- 
With Regards,
Amit Kapila.

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Fix a race condition in updating procArray->replication_slot_xmin.

  2. Don't retreat slot's confirmed_flush LSN.

  3. Add additional checks while creating the initial decoding snapshot.