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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 19:14:59
Message-ID: AANLkTi=A0pDdmCb-tjA0=pusZcXDp6SF5YviAcWrhb6r@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Mon, Feb 28, 2011 at 2:01 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 1:45 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>> 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.
>
> Possibly, but it's not clear to me that this patch fixes that.
> As I said, it's no longer obvious what the patch means to do, and I'd
> like a clear statement of that.

Fair enough.  I assume Marko will provide that shortly.  I believe the
consensus was to make the regular case behave like EXPLAIN ANALYZE
rather than the other way around...

>> So in theory you could turn on auto_explain and have
>> the semantics of your queries change.  That would be Bad.
>
> That's just FUD.  auto_explain doesn't run EXPLAIN ANALYZE.

Oh, woops.  I stand corrected.  But I guess the query might behave
differently with and without EXPLAIN ANALYZE?

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

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