From: Tom Lane <tgl@sss.pgh.pa.us>
To: Noah Misch <noah@leadboat.com>
cc: Michael Paquier <michael@paquier.xyz>, pgsql-hackers@postgresql.org
Subject: Re: XLogReadRecord() error in XlogReadTwoPhaseData()
In-reply-to: <20211112012234.GA1020314@rfd.leadboat.com>
References: <20211107013157.GB790288@rfd.leadboat.com>
 <YYiqxtEqhgb5gIWL@paquier.xyz> <20211112012234.GA1020314@rfd.leadboat.com>
Comments: In-reply-to Noah Misch <noah@leadboat.com>
	message dated "Thu, 11 Nov 2021 17:22:34 -0800"
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Date: Wed, 17 Nov 2021 17:47:10 -0500
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Noah Misch <noah@leadboat.com> writes:
> Tom Lane reported another instance today:
> https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=3Dtadarida&dt=3D=
2021-11-11%2013%3A29%3A58

> Each of the three failures happened on a sparc64 Debian+gcc machine.  I =
had
> tried ~8000 iterations on thorntail, another sparc64 Debian+gcc animal,
> without reproducing this.

>>> As a first step, let's report the actual XLogReadRecord() error messag=
e.
>>> Attached.

>> Good catch!  This looks good.

> Pushed.

Well, we didn't have to wait too long [1]:

#   at t/003_cic_2pc.pl line 143.
#                   'pgbench: error: client 0 script 1 aborted in command =
4 query 0: ERROR:  could not read two-phase state from WAL at 0/159EF88: u=
nexpected pageaddr 0/0 in log segment 000000010000000000000001, offset 589=
0048
# pgbench: error: client 2 script 3 aborted in command 2 query 0: ERROR:  =
canceling statement due to lock timeout
# pgbench: fatal: Run was aborted; the above results are incomplete.

I suppose "unexpected pageaddr 0/0" is most easily explained by supposing
that XlogReadTwoPhaseData tried to read a WAL page that hadn't been
written out yet.  Have we got any synchronization around that?

			regards, tom lane

[1] https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=3Dtadarida&dt=3D=
2021-11-17%2013%3A01%3A24