From: | Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> |
---|---|
To: | Andres Freund <andres(at)anarazel(dot)de> |
Cc: | depesz(at)depesz(dot)com, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, pgsql-bugs mailing list <pgsql-bugs(at)postgresql(dot)org> |
Subject: | Re: WAL segments removed from primary despite the fact that logical replication slot needs it. |
Date: | 2022-11-17 14:22:12 |
Message-ID: | CAD21AoCjKKtQjEma7LR3iKiwW1tzJ8yK4gWdr0p1g2SMKU1Axg@mail.gmail.com |
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On Thu, Nov 17, 2022 at 5:03 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> Hi,
>
> On 2022-11-15 23:59:37 +0900, Masahiko Sawada wrote:
> > > Is something like the following scenario possible to happen?
> > >
> > > 1. wal sender updates slot's restart_lsn and releases the spin lock
> > > (not saved in the disk yet)
> > > 2. someone updates slots' minimum restart_lsn (note that slot's
> > > restart_lsn in memory is already updated).
>
> You mean ReplicationSlotsComputeRequiredLSN(), or update that specific slot's
> restart_lsn? The latter shouldn't happen.
I meant the former.
>
>
> > > 3. checkpointer removes WAL files older than the minimum restart_lsn
> > > calculated at step 2.
>
> For xmin we have protection against that via the split between
> catalog_xmin/effective_catalog_xmin. We should probably mirror that for
> restart_lsn as well.
>
> We should also call ReplicationSlotsComputeRequiredLSN if only update_restart
> is true...
Agree.
>
>
> > > 4. wal sender restarts for some reason (or server crashed).
>
> I don't think walsender alone restarting should change anything, but
> crash-restart obviously would.
Right. I've confirmed this scenario is possible to happen with crash-restart.
Regards,
--
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com
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