Horton

Re: BUG #17072: Assert for clogGroupNext failed due to a race condition in TransactionGroupUpdateXidStatus()

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Alexander Lakhin <exclusion@gmail.com>, PostgreSQL mailing lists <pgsql-bugs@lists.postgresql.org>
Date: 2021-06-25T09:55:13Z
Lists: pgsql-bugs 
On Fri, Jun 25, 2021 at 12:20 AM PG Bug reporting form
<noreply@postgresql.org> wrote:
>
> The offending (the one that leaved a "valid" clogGroupNext) proccess is
> 60d48c2d.ea21. It looks like it got from the
> pg_atomic_compare_exchange_u32() the nextidx value that was written in the
> clogGroupFirst by the process 60d48c2e.ebc5, and exited just after that.
>

Your analysis seems to be in the right direction. Can you try by
setting clogGroupNext to INVALID_PGPROCNO
(pg_atomic_write_u32(&proc->clogGroupNext, INVALID_PGPROCNO);) before
we return false in the first while(true) loop in function
TransactionGroupUpdateXidStatus()?

I think this should be reproducible on all branches from HEAD till
v11. Have you tried in any other branch? I'll also try to reproduce
it.

-- 
With Regards,
Amit Kapila.

Commits

  1. Fix race condition in TransactionGroupUpdateXidStatus().