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Re: Writeable CTEs and empty relations

From: Marko Tiikkaja <marko(dot)tiikkaja(at)cs(dot)helsinki(dot)fi>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Writeable CTEs and empty relations
Date: 2010-02-10 22:50:48
Message-ID: 4B733848.3000107@cs.helsinki.fi (view raw or flat)
Thread:
Lists: pgsql-hackers
On 2010-02-10 23:57 +0200, Tom Lane wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> If the executor has buried in it the assumption that the snapshot
>> can't change after startup, then does that mean that we need to start
>> up and shut down the executor for each subquery?
> 
> Yes, I think so.  That's the way it's always worked in the past;
> see for example PortalRunMulti() and ProcessQuery().  I think trying
> to change that is a high-risk, low-reward activity.
> 
> This probably means that the planner output for queries involving
> writeable CTEs has to be a separate PlannedStmt per such CTE.

I'm looking at this, but I can't think of any good way of associating
the tuplestores from PortalRunMulti() with the correct CTEs.  Any ideas?


Regards,
Marko Tiikkaja

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