Re: WITH RECUSIVE patches 0723

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Andrew Dunstan <andrew(at)dunslane(dot)net>
Cc: Martijn van Oosterhout <kleptog(at)svana(dot)org>, Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: WITH RECUSIVE patches 0723
Date: 2008-07-28 23:18:14
Message-ID: 395.1217287094@sss.pgh.pa.us
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Andrew Dunstan <andrew(at)dunslane(dot)net> writes:
> Tom Lane wrote:
>> My thought is that we could optimize away materialization in cases where
>> we can tell it's not needed (no volatile functions and/or no multiple
>> scans of the subquery). But not being able to do it means we've
>> implemented the feature incorrectly.

> I'm not sure how much work that would involve, but none of this means we
> can't have the feature for 8.4, right? Just that there is more work to do.

I would be *extremely* surprised if we don't find ourselves improving
the optimization of WITH clauses long after 8.4. We're still working on
outer joins, remember ;-). My point here is just that the base case
before optimization has to behave per spec. Optimizing more later is
good, fixing deliberately introduced non-compliance not so good.

regards, tom lane

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