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: 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: 2021-11-23T20:40:35Z
Lists: pgsql-hackers 
On 2021-Nov-23, Tom Lane wrote:

> We're *still* not out of the woods with 026_overwrite_contrecord.pl,
> as we are continuing to see occasional "mismatching overwritten LSN"
> failures, further down in the test where it tries to start up the
> standby:

Augh.

> Looking at adjacent successful runs, it seems that the exact point
> where the "missing contrecord" starts varies substantially, even after
> our previous fix to disable autovacuum in this test.  How could that be?

Well, there is intentionally some variability.  Maybe not as much as one
would wish, but I expect that that should explain why that point is not
always the same.

> It's probably for the best though, because I think this is exposing
> an actual bug that we would not have seen if the start point were
> completely consistent.  I have not dug into the code, but it looks to
> me like if the "consistent recovery state" is reached exactly at a
> page boundary (0/1FFE000 in all these cases), then the standby expects
> that to be what the OVERWRITE_CONTRECORD record will point at.  But
> actually it points to the first WAL record on that page, resulting
> in a bogus failure.

So what is happening is that we set state->overwrittenRecPtr to the LSN
of page start, ignoring the page header.  Is that the LSN of the first
record in a page?  I'll see if I can reproduce the problem.

-- 
Álvaro Herrera           39°49'30"S 73°17'W  —  https://www.EnterpriseDB.com/
"La persona que no quería pecar / estaba obligada a sentarse
 en duras y empinadas sillas    / desprovistas, por cierto
 de blandos atenuantes"                          (Patricio Vogel)

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