Date: Mon, 18 Jun 2018 14:04:19 -0400
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Antonin Houska <ah@cybertec.at>
Cc: Arseny Sher <a.sher@postgrespro.ru>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Fix slot's xmin advancement and subxact's lost snapshots in
 decoding.
Message-ID: <20180618180419.mysc6nxvntgvfgg2@alvherre.pgsql>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <15387.1528700867@localhost>
User-Agent: NeoMutt/20170306-137-4415bd-dirty (1.8.0)
Precedence: bulk

On 2018-Jun-11, Antonin Houska wrote:

> Arseny Sher <a.sher@postgrespro.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().

I've been going over this patch also, and I've made a few minor edits of
the patch and the existing code as I come to understand what it's all
about.

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

Please don't.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services