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From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Nikhil Sontakke <nikhils@2ndquadrant.com>
Cc: David Steele <david@pgmasters.net>
Cc: Andres Freund <andres@anarazel.de>
Cc: Andrew Dunstan <andrew.dunstan@2ndquadrant.com>
Cc: Simon Riggs <simon@2ndquadrant.com>
Cc: Craig Ringer <craig@2ndquadrant.com>
Cc: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
Cc: Petr Jelinek <petr.jelinek@2ndquadrant.com>
Cc: Sokolov Yura <y.sokolov@postgrespro.ru>
Cc: Stas Kelvich <s.kelvich@postgrespro.ru>
Cc: Dmitry Dolgov <9erthalion6@gmail.com>
Cc: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] logical decoding of two-phase transactions
Date: Mon, 16 Jul 2018 19:38:28 +0200
Message-ID: <ad722d03-4468-b5f7-8c59-8ac79ff3c2d0@2ndquadrant.com> (raw)
In-Reply-To: <15404.1531761677@sss.pgh.pa.us>
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	<15404.1531761677@sss.pgh.pa.us>

On 07/16/2018 07:21 PM, Tom Lane wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> I agree.  As a general statement, I think the idea of trying to
>> prevent transactions from aborting is really scary.  It's almost an
>> axiom of the system that we're always allowed to abort, and I think
>> there could be a lot of unintended and difficult-to-fix consequences
>> of undermining that guarantee.  I think it will be very difficult to
>> create a sound system for delaying transactions, and I doubt very much
>> that the proposed system is sound.
> 
> Ugh, is this patch really dependent on such a thing?
> 

Unfortunately it does :-( Without it the decoding (or output plugins) 
may see catalogs broken in various ways - the catalog records may get 
vacuumed, HOT chains are broken, ... There were attempts to change that 
part, but that seems an order of magnitude more invasive than this.

> TBH, I think the odds of making that work are indistinguishable from zero;
> and even if you managed to commit something that did work at the instant
> you committed it, the odds that it would stay working in the face of later
> system changes are exactly zero.  I would reject this idea out of hand.
> 

Why? How is this significantly different from other patches touching 
ProcArray and related bits?


regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services




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