Horton

Re: prevent immature WAL streaming

Amul Sul <sulamul@gmail.com>

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From: Amul Sul <sulamul@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Alvaro Herrera <alvherre@alvh.no-ip.org>, Andres Freund <andres@anarazel.de>, Andrew Dunstan <andrew@dunslane.net>, "Bossart, Nathan" <bossartn@amazon.com>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>, "masao.fujii@oss.nttdata.com" <masao.fujii@oss.nttdata.com>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>, "mengjuan.cmj@alibaba-inc.com" <mengjuan.cmj@alibaba-inc.com>, "Jakub.Wartak@tomtom.com" <Jakub.Wartak@tomtom.com>, Ryo Matsumura <matsumura.ryo@fujitsu.com>
Date: 2021-11-26T04:24:30Z
Lists: pgsql-hackers 
On Fri, Nov 26, 2021 at 1:42 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> Alvaro Herrera <alvherre@alvh.no-ip.org> writes:
> > On 2021-Nov-25, Tom Lane wrote:
> >> Really?  AFAICS the WAL record contains the correct value, or at least
> >> we should define that one as being correct, for precisely this reason.
>
> > I don't know what is the correct value for a record that comes exactly
> > after the page header.  But here's a patch that fixes the problem; and
> > if a standby replays WAL written by an unpatched primary, it will be
> > able to read past instead of dying of FATAL.
>
> Meh ... but given the simplicity of the write-side fix, maybe changing
> it is appropriate.
>
> However, this seems too forgiving:
>
> +    if (xlrec->overwritten_lsn != state->overwrittenRecPtr &&
> +        xlrec->overwritten_lsn - SizeOfXLogShortPHD != state->overwrittenRecPtr &&
> +        xlrec->overwritten_lsn - SizeOfXLogLongPHD != state->overwrittenRecPtr)
>

Unless I am missing something, I am not sure why need this adjustment
if we are going to use state->currRecPtr value which doesn't seem to
be changing at all. AFAICU, state->currRecPtr will be unchanged value
whether going to set overwrittenRecPtr or abortedRecPtr. Do primary
and standby see state->currRecPtr differently, I guess not, never?

Regards,
Amul

Commits

  1. Fix determination of broken LSN in OVERWRITTEN_CONTRECORD

  2. Fix instability in 026_overwrite_contrecord.pl test.

  3. Fix typo

  4. Change recently added test code for stability

  5. Remove unstable, unnecessary test; fix typo

  6. Repair two portability oversights of new test

  7. Fix WAL replay in presence of an incomplete record

  8. Document XLOG_INCLUDE_XID a little better

  9. Revert "Avoid creating archive status ".ready" files too early"

  10. Avoid creating archive status ".ready" files too early

  11. Fix scenario where streaming standby gets stuck at a continuation record.

  12. Teach xlogreader to follow timeline switches

  13. Forbid using pg_xlogfile_name() and pg_xlogfile_name_offset() during