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Re: Writeable CTEs and empty relations

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Marko Tiikkaja <marko(dot)tiikkaja(at)cs(dot)helsinki(dot)fi>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Writeable CTEs and empty relations
Date: 2010-02-10 01:20:52
Message-ID: 1977.1265764852@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Marko Tiikkaja <marko(dot)tiikkaja(at)cs(dot)helsinki(dot)fi> writes:
> On 2010-02-10 02:19 +0200, Tom Lane wrote:
>> You still haven't explained why it's a good idea to change the snapshot
>> after the executor has started.  Right at the moment I'm prepared to
>> reject the patch on that ground alone.

> The patch only touches the snapshot's curcid.  That's needed to allow
> the queries see the tuples of the DML WITHs ran before that particular
> query.

... and they will also see, for example, tuples inserted by triggers
fired by those queries.  I thought the plan for this feature was to
store and re-read the RETURNING data, not to go back and re-read the
underlying tables.

			regards, tom lane

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