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Re: Review: Fix snapshot taking inconsistencies

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Marko Tiikkaja <marko(dot)tiikkaja(at)cs(dot)helsinki(dot)fi>, Steve Singer <ssinger_pg(at)sympatico(dot)ca>, pgsql-hackers(at)postgresql(dot)org, Alvaro Herrera <alvherre(at)commandprompt(dot)com>
Subject: Re: Review: Fix snapshot taking inconsistencies
Date: 2011-02-28 18:58:17
Message-ID: AANLkTimAYWz36fGpXTmWUZXr0QGYawzb5G-z-q2jmTAp@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Mon, Feb 28, 2011 at 1:45 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> On Mon, Feb 28, 2011 at 1:22 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>> So: exactly what is the intended behavioral change as of now, and what
>>> is the argument supporting that change?
>
>> IIUC, this is the result of countless rounds of communal bikeshedding around:
>
> Quite :-(.  But I'm not sure where the merry-go-round stopped.
>
>> http://archives.postgresql.org/pgsql-hackers/2010-07/msg01256.php
>
> Please notice that the very terms of discussion in that message depend
> on a view of wCTEs that has got nothing to do with what was applied.
> I'm afraid that the goals of this patch might be similarly obsolete.

No, I don't think so.  IIUC, the problem is that EXPLAIN ANALYZE runs
the rewrite products with different snapshot handling than the regular
execution path.  So in theory you could turn on auto_explain and have
the semantics of your queries change.  That would be Bad.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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