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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 00:19:56
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Lists: pgsql-hackers
Marko Tiikkaja <marko(dot)tiikkaja(at)cs(dot)helsinki(dot)fi> writes:
> On 2010-02-08 21:30 +0200, I wrote:
>> This doesn't exactly work anymore since we modify the snapshot after
>> calling ExecInitScan().  I'm not really familiar with this part of the
>> code, so I'm asking: is there a simple enough way around this?  Would
>> updating scan->rs_nblocks before scanning the first tuple be OK?

> I've looked at this some more, and the problem is a lot bigger than I
> originally thought.  We'd basically be forced to do another initscan()
> before starting a new scan after the snapshot changed.  One way to
> accomplish this would be that ExecutePlan() would leave a flag in EState
> whenever the scan nodes need to reinit.

> Does this sound completely unacceptable?

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.

			regards, tom lane

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Subject: Re: Writeable CTEs and empty relations
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