| From: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
|---|---|
| To: | Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> |
| Cc: | Andres Freund <andres(at)anarazel(dot)de>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, kuroda(dot)hayato(at)fujitsu(dot)com, Thomas Munro <thomas(dot)munro(at)gmail(dot)com> |
| Subject: | Re: Assertion failure in SnapBuildInitialSnapshot() |
| Date: | 2023-01-27 05:24:55 |
| Message-ID: | CAA4eK1LBJm48515uAoSqiD-qHxXQO9-nAVzps5U73abrrtdFVw@mail.gmail.com |
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On Thu, Dec 8, 2022 at 8:17 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
> The same assertion failure has been reported on another thread[1].
> Since I could reproduce this issue several times in my environment
> I've investigated the root cause.
>
> I think there is a race condition of updating
> procArray->replication_slot_xmin by CreateInitDecodingContext() and
> LogicalConfirmReceivedLocation().
>
> What I observed in the test was that a walsender process called:
> SnapBuildProcessRunningXacts()
> LogicalIncreaseXminForSlot()
> LogicalConfirmReceivedLocation()
> ReplicationSlotsComputeRequiredXmin(false).
>
> In ReplicationSlotsComputeRequiredXmin() it acquired the
> ReplicationSlotControlLock and got 0 as the minimum xmin since there
> was no wal sender having effective_xmin.
>
What about the current walsender process which is processing
running_xacts via SnapBuildProcessRunningXacts()? Isn't that walsender
slot's effective_xmin have a non-zero value? If not, then why?
--
With Regards,
Amit Kapila.
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