Horton

Re: prevent immature WAL streaming

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

View thread View on postgr.es
From: "alvherre@alvh.no-ip.org" <alvherre@alvh.no-ip.org>
To: "Bossart, Nathan" <bossartn@amazon.com>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.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>
Date: 2021-08-24T23:01:27Z
Lists: pgsql-hackers

Attachments

On 2021-Aug-24, Bossart, Nathan wrote:

> I wonder if we need to move the call to RegisterSegmentBoundary() to
> somewhere before WALInsertLockRelease() for this to work as intended.
> Right now, boundary registration could take place after the flush
> pointer has been advanced, which means GetSafeFlushRecPtr() could
> still return an unsafe position.

Yeah, you're right -- that's a definite risk.  I didn't try to reproduce
a problem with that, but it is seems pretty obvious that it can happen.

I didn't have a lot of luck with a reliable reproducer script.  I was
able to reproduce the problem starting with Ryo Matsumura's script and
attaching a replica; most of the time the replica would recover by
restarting from a streaming position earlier than where the problem
occurred; but a few times it would just get stuck with a WAL segment
containing a bogus record.  Then, after patch, the problem no longer
occurs.

I attach the patch with the change you suggested.

-- 
Álvaro Herrera              Valdivia, Chile  —  https://www.EnterpriseDB.com/
Tom: There seems to be something broken here.
Teodor: I'm in sackcloth and ashes...  Fixed.
        http://archives.postgresql.org/message-id/482D1632.8010507@sigaev.ru

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