Re: wCTE behaviour

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: David Fetter <david(at)fetter(dot)org>, Peter Eisentraut <peter_e(at)gmx(dot)net>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Robert Haas <robertmhaas(at)gmail(dot)com>, Yeb Havinga <yebhavinga(at)gmail(dot)com>, Hitoshi Harada <umi(dot)tanuki(at)gmail(dot)com>
Subject: Re: wCTE behaviour
Date: 2011-02-24 23:36:03
Message-ID: 2314.1298590563@sss.pgh.pa.us
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Marko Tiikkaja <marko(dot)tiikkaja(at)cs(dot)helsinki(dot)fi> writes:
> I fixed an issue with the portal logic, and now we use
> PORTAL_ONE_RETURNING for wCTE queries, even if the main query is not a
> DML or does not have RETURNING. This also means that we materialize the
> results of the main query sometimes unnecessarily, but that doesn't look
> like an easy thing to fix. PORTAL_ONE_RETURNING as a name is also a bit
> misleading now, so maybe that needs changing..

Why is it necessary to hack the portal logic at all? The patch seems to
work for me without that. (I've fixed quite a few bugs though, so maybe
what this is really doing is masking a problem elsewhere.)

Also, why are we forbidding wCTEs in cursors? Given the current
definitions, that case seems to work fine too: the wCTEs will be
executed as soon as you fetch something from the cursor. Are you
just worried about not allowing a case that might be hard to support
later?

regards, tom lane

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