Re: upper planner path-ification

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, "pgsql-hackers\(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: upper planner path-ification
Date: 2015-05-18 14:12:04
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Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk> writes:
> Incidentally, the most obvious obstacle to better planning of grouping
> sets in the sorted cases is not so much how to pick paths in
> grouping_planner itself, but rather the fact that query_planner wants to
> be given only one sort order. Is there any prospect for improvement
> there?

Hm. That's a hangover from when query_planner also gave back a Plan
(singular) rather than a set of Paths. I don't see any fundamental reason
why we couldn't generalize it to be a list of potentially useful output
orderings rather than just one. But I'm a bit concerned about the ensuing
growth in planning time; is it really all that useful?

regards, tom lane

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