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

Hello Amit,
25.06.2021 12:55, Amit Kapila wrote:
> 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()?
With this modification that assert is not triggered, all 100 iterations
pass fine (triple checked).
> 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.
I've reproduced it on REL_11_STABLE, REL_12_STABLE, REL_13_STABLE, and
master.

Best regards,
Alexander