| 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 |
| Message-ID: | 12179.1431958324@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
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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