On Fri, Mar 02, 2012 at 03:45:38PM -0500, Robert Haas wrote: > SELECT SUM(1) FROM (SELECT * FROM randomtext ORDER BY t) x; > > On unpatched master, this takes about 416 ms (plus or minus a few). > With the attached patch, it takes about 389 ms (plus or minus a very > few), a speedup of about 7%. > > I repeated the experiment using the C locale, like this: > > SELECT SUM(1) FROM (SELECT * FROM randomtext ORDER BY t COLLATE "C") x; > > Here, it takes about 202 ms with the patch, and about 231 ms on > unpatched master, a savings of about 13%.
> [oprofile report, further discussion] Thanks for looking into this. Your patch is also a nice demonstration of sortsupport's ability to help with more than just fmgr overhead. > Considering all that, I > had hoped for more like a 15-20% gain from this approach, but it > didn't happen, I suppose because some of the instructions saved just > resulted in more processor stalls. All the same, I'm inclined to > think it's still worth doing. This is a border case, but I suggest that a 13% speedup on a narrowly-tailored benchmark, degrading to 7% in common configurations, is too meager to justify adopting this patch. nm -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers