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: Amul Sul <sulamul@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, 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: 2021-11-25T18:30:20Z
Lists: pgsql-hackers 
On 2021-Nov-25, Amul Sul wrote:

> In XLogReadRecord(), both the variables being compared have
> inconsistency in the assignment -- one gets assigned from
> state->currRecPtr where other is from RecPtr.
> 
> .....
> state->overwrittenRecPtr = state->currRecPtr;
> .....
> state->abortedRecPtr = RecPtr;
> .....
> 
> Before the place where assembled flag sets, there is a bunch of code
> that adjusts RecPtr. I think instead of  RecPtr, the latter assignment
> should use state->currRecPtr as well.

You're exactly right.  I managed to reproduce the problem shown by
buildfarm members, and indeed this fixes it.  And it makes sense: the
adjustment you refer to, is precisely to skip the page header when the
LSN is the start of the page, which is exactly the problem we're seeing
in the buildfarm ... except that on lapwing branch REL_11_STABLE, we're
seeing the LSN is off by 0x14 instead of 0x18.  That seems very strange.
I think the reason for this is that lapwing has MAXALIGN 4, so
MAXALIGN(sizeof(XLogPageHeaderData)) is 20, not 24 as is the case in the
other failing members.

... checks buildfarm ...

Yeah, all the others in Tom's list are x86-64.

I'm pushing the fix in a minute.

-- 
Álvaro Herrera         PostgreSQL Developer  —  https://www.EnterpriseDB.com/
"¿Qué importan los años?  Lo que realmente importa es comprobar que
a fin de cuentas la mejor edad de la vida es estar vivo"  (Mafalda)

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