Horton

Re: prevent immature WAL streaming

Alvaro Herrera <alvherre@alvh.no-ip.org>

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From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Amul Sul <sulamul@gmail.com>, 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: 2021-11-25T19:58:28Z
Lists: pgsql-hackers

Attachments

On 2021-Nov-25, Tom Lane wrote:

> Alvaro Herrera <alvherre@alvh.no-ip.org> writes:
> 
> > The problem is that the bug occurs while writing the WAL record.  Fixed
> > servers won't produce such records, but if you run an unpatched server
> > and it happens to write one, without a mitigation you cannot get away
> > from FATAL during replay.
> 
> 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.

I originally wrote this to have a WARNING in VerifyOverwriteContrecord
(in the cases that are new), with the idea that it'd prompt people to
upgrade, but that's probably a waste of time.

-- 
Álvaro Herrera              Valdivia, Chile  —  https://www.EnterpriseDB.com/
"El hombre nunca sabe de lo que es capaz hasta que lo intenta" (C. Dickens)

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