Re: WAL logging problem in 9.4.3?

From: Martijn van Oosterhout <kleptog(at)svana(dot)org>
To: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Cc: Andres Freund <andres(at)anarazel(dot)de>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: WAL logging problem in 9.4.3?
Date: 2015-07-03 06:01:37
Message-ID: 20150703060137.GB20285@svana.org
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On Fri, Jul 03, 2015 at 02:34:44PM +0900, Fujii Masao wrote:
> > Hmm, for me it is 100% reproducable. Are you familiar with Docker? I
> > can probably construct a Dockerfile that reproduces it pretty reliably.
>
> I could reproduce the problem in the master branch by doing
> the following steps.

Thank you, I wasn't sure if you could kill the server fast enough
without containers, but it looks like immediate mode is enough.

> 1. start the PostgreSQL server with wal_level = minimal
> 2. execute the following SQL statements
> begin;
> create table test(id serial primary key);
> truncate table test;
> commit;
> 3. shutdown the server with immediate mode
> 4. restart the server (crash recovery occurs)
> 5. execute the following SQL statement
> select * from test;
>
> The optimization of TRUNCATE opereation that we can use when
> CREATE TABLE and TRUNCATE are executed in the same transaction block
> seems to cause the problem. In this case, only index file truncation is
> logged, and index creation in btbuild() is not logged because wal_level
> is minimal. Then at the subsequent crash recovery, index file is truncated
> to 0 byte... Very simple fix is to log an index creation in that case,
> but not sure if that's ok to do..

Looks plausible to me.

For reference I attach a small tarball for reproduction with docker.

1. Unpack tarball into empty dir (it has three small files)
2. docker build -t test .
3. docker run -v /tmp/pgtest:/data test
4. docker run -v /tmp/pgtest:/data test

Data dir is in /tmp/pgtest

Have a nice day,
--
Martijn van Oosterhout <kleptog(at)svana(dot)org> http://svana.org/kleptog/
> He who writes carelessly confesses thereby at the very outset that he does
> not attach much importance to his own thoughts.
-- Arthur Schopenhauer

Attachment Content-Type Size
postgresql-test.tgz application/x-gtar 987 bytes

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