Re: Fix slot's xmin advancement and subxact's lost snapshots in decoding.

From: Antonin Houska <ah(at)cybertec(dot)at>
To: Arseny Sher <a(dot)sher(at)postgrespro(dot)ru>
Cc: pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Fix slot's xmin advancement and subxact's lost snapshots in decoding.
Date: 2018-06-11 07:07:47
Message-ID: 15387.1528700867@localhost
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Arseny Sher <a(dot)sher(at)postgrespro(dot)ru> wrote:
> Please see detailed description of the issues, tests which reproduce
> them and fixes in the attached patch.

I've played with your tests and gdb for a while, both w/o and with your
patch. I think I can understand both problems. I could not invent simpler way
to fix them.

One comment about the coding: since you introduce a new transaction list and
it's sorted by LSN, I think you should make the function AssertTXNLsnOrder()
more generic and use it to check the by_base_snapshot_lsn list too. For
example call it after the list insertion and deletion in
ReorderBufferPassBaseSnapshot().

Also I think it makes no harm if you split the diff into two, although both
fixes use the by_base_snapshot_lsn field.

--
Antonin Houska
Cybertec Schönig & Schönig GmbH
Gröhrmühlgasse 26, A-2700 Wiener Neustadt
Web: https://www.cybertec-postgresql.com

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