From: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
---|---|
To: | Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> |
Cc: | depesz(at)depesz(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: | 2022-11-15 04:51:18 |
Message-ID: | CAA4eK1JmV90sqy9si9jWEovHruvA5EP8FbnjNTQFOmHmy0Z3vw@mail.gmail.com |
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On Tue, Nov 15, 2022 at 7:50 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
> On Fri, Nov 11, 2022 at 11:50 PM hubert depesz lubaczewski
> <depesz(at)depesz(dot)com> wrote:
> >
> > 2022-11-10 20:59:55 UTC 103A7/7B666388 focal14 pgoutput logical 16607 canvas f t 10414 \N 3241434855 1039D/83825958 1039D/8DECBA18
> > 2022-11-10 21:00:54 UTC 103A7/88225C28 focal14 pgoutput logical 16607 canvas f t 10414 \N 3241434855 1039D/83825958 1039D/911A8DB0
> > 2022-11-10 21:01:53 UTC 103A7/9E77EF90 focal14 pgoutput logical 16607 canvas f f \N \N 3241434855 1039D/83825958 1039D/911A8DB0
> > 2022-11-10 21:02:52 UTC 103A7/B45ECEA8 focal14 pgoutput logical 16607 canvas f f \N \N 3241434855 1039D/83825958 1039D/911A8DB0
> > 2022-11-10 21:03:52 UTC 103A7/C4355F60 focal14 pgoutput logical 16607 canvas f t 21748 \N 3241443528 1039D/83825958 1039D/955633D0
> > 2022-11-10 21:04:51 UTC 103A7/D5A6FDD8 focal14 pgoutput logical 16607 canvas f t 21748 \N 3241443528 1039D/83825958 1039D/96453F38
> > 2022-11-10 21:05:50 UTC 103A7/E2C7F590 focal14 pgoutput logical 16607 canvas f f \N \N 3241443528 1039D/83825958 1039D/96453F38
> > 2022-11-10 21:06:49 UTC 103A7/F28B2000 focal14 pgoutput logical 16607 canvas f f \N \N 3241443528 1039D/83825958 1039D/96453F38
> > 2022-11-10 21:07:48 UTC 103A8/3828D20 focal14 pgoutput logical 16607 canvas f f \N \N 3241443528 1039D/83825958 1039D/96453F38
> > 2022-11-10 21:08:47 UTC 103A8/15BBF088 focal14 pgoutput logical 16607 canvas f f \N \N 3241443528 1039D/83825958 1039D/96453F38
>
> It happened twice that the walsender process was active for at least
> one minute while not advancing restart_lsn and exited. Could you share
> the server logs from around 2022-11-10 20:59:55 to 21:08:47 so that we
> can find out what the wal sender processes were doing?
>
> Also, you may have logs for "failed to increase restart lsn: proposed
> %X/%X, after %X/%X, current candidate %X/%X, current after %X/%X,
> flushed up to %X/%X" and "got new restart lsn %X/%X at %X/%X". If so,
> please share it as well.
>
> I've tried to reproduce this issue with a similar setting in a loop
> but could not.
>
> Given that you have the log "attempting to remove WAL segments older
> than log file 000000000001039D0000008A", the last WAL file we need to
> retain calculated by KeepLogSeg() was wrong.
>
> KeepLogSeg() retreated the last segment that we need to retain while
> considering replication slots' minimum LSN (and wal_keep_segments) but
> it seemed not to work fine. The possibilities are (1) we got the wrong
> slots' minimum LSN that is newer than a slot's LSN (ie, retreated
> logSegNo but it's still newer than required WAL files) or (2) we got
> an invalid slots's minimum LSN (ie, didn't retreated at all). If we
> know what the RedoRecPtr was, we can calculate _logSegNo that has not
> been retreated by KeepLogSeg().
>
The other possibility is that the slot is not considered for minimum
LSN computation (say in_use flag is temporarily set to false).
> BTW in LogicalConfirmReceivedLocation(), we set restart_lsn as follows:
>
> if (MyReplicationSlot->candidate_restart_valid != InvalidXLogRecPtr &&
> MyReplicationSlot->candidate_restart_valid <= lsn)
> {
> Assert(MyReplicationSlot->candidate_restart_lsn !=
> InvalidXLogRecPtr);
>
> MyReplicationSlot->data.restart_lsn =
> MyReplicationSlot->candidate_restart_lsn;
> MyReplicationSlot->candidate_restart_lsn = InvalidXLogRecPtr;
> MyReplicationSlot->candidate_restart_valid = InvalidXLogRecPtr;
> updated_restart = true;
> }
>
> Is it worth changing the assertion to elog(ERROR) so that we can
> detect that an invalid value is set to restart_lsn?
>
This is worth considering but note that the caller of this has an
assertion for invalid values being assigned to candidate_restart_*
variables. Also, wouldn't be shown as invalid for restart_lsn in
pg_replication_slots?
--
With Regards,
Amit Kapila.
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