"Joshua D. Drake" <jd@commandprompt.com> writes:
> Let me know what you come up with. Thanks for the help.
Hmph. On my FC3 machine, 7.4 is consistently faster than 7.3 in sorting
and grouping this data --- it's about 710 vs 960 msec. (This is on a P4
1.8GHz, presumably slower than your machines.) So there's no
algorithmic change that might be biting us. It seems we have to look at
the platforms involved. At this point I can think of two hypotheses
that haven't been eliminated:1. FC1's qsort is much faster than FC3's on this case.2. The 64-bit build has got some
kindof performance problem that's not generic to 7.4.*.
#1 doesn't seem very probable, though it's possible. I think what you
should do next is build 7.3 on the 64-bit machine and see what performance
it's got. You might also try non-64-bit builds and see what they do.
Just FYI, you can test the behavior without loading your full database
--- just load the data you sent me and do
explain analyze
select count(*) from foo
group by post_id, topic_id, topic_title, topic_status, topic_replies, topic_time, topic_type,
topic_vote, topic_last_post_id, forum_name, forum_status, forum_id, auth_view, auth_read, auth_post,
auth_reply, auth_edit, auth_delete, auth_sticky, auth_announce, auth_pollcreate, auth_vote,
auth_attachments
;
On 7.4 and up you may have to set enable_hashagg = off to force a
Sort/GroupAggregate plan instead of HashAggregate.
regards, tom lane