>>>>> "Tom" == Tom Lane <tgl@sss.pgh.pa.us> writes:
Tom> Hm. That's a hangover from when query_planner also gave back aTom> Plan (singular) rather than a set of Paths. I
don'tsee anyTom> fundamental reason why we couldn't generalize it to be a list ofTom> potentially useful output
orderingsrather than just one. But I'mTom> a bit concerned about the ensuing growth in planning time; is itTom> really
allthat useful?
The planning time growth is a possible concern, yes. The potential gain
is eliminating one sort step, in the case when the input has a usable
sorted path but grouping_planner happens not to ask for it (when there's
more than just a single rollup, the code currently asks for one of the
sort orders pretty much arbitrarily since it has no real way to know
otherwise). Whether that would justify it... I don't know. Maybe that's
one to save for later to see if there's any feedback from actual use.
--
Andrew (irc:RhodiumToad)
