Yeah, the problem doesn't appear to be there. As I said, if I look at
the PS of the system when its bogging, there aren't a whole bunch of
processes stuck doing these, so while this does take a second or two to
come back, that's not that bad.
Its GENERAL performance that just bites - the system is obviously out of
CPU, but what I can't get a handle on is WHY. It does not appear to be
accumulating large amounts of runtime in processes I can catch, but the
load average is quite high.
This is why I'm wondering if what I'm taking here is a hit on the
fork/exec inside the portmaster, in the setup internally in there, in
the IPC between my process via libPQ, etc - and how I can profile what's
going on.
Karl Denninger ([EMAIL PROTECTED])
http://www.denninger.net
Tom Lane wrote:
Karl Denninger <[EMAIL PROTECTED]> writes:
But.... here's the query that has a habit of taking the most time....
select forum, * from post where toppost = 1 and (replied > (select
lastview from forumlog where login='theuser' and forum=post.forum and
number is null)) is not false AND (replied > (select lastview from
forumlog where login='theuser' and forum=post.forum and
number=post.number)) is not f
alse order by pinned desc, replied desc offset 0 limit 20
Did that ever perform well for you? It's the sub-selects that are
likely to hurt ... in particular,
-> Index Scan using post_top on post (cost=0.00..57266.37
rows=113 width=757)
Index Cond: (toppost = 1)
Filter: (((replied > (subplan)) IS NOT FALSE) AND
((replied > (subplan)) IS NOT FALSE))
versus
Index Scan using post_top on post (cost=0.00..632.03 rows=1013 width=11)
Index Cond: (toppost = 1)
The planner thinks that the two subplan filter conditions will eliminate
about 90% of the rows returned by the bare indexscan (IIRC this is
purely a rule of thumb, not based on any statistics) and that testing
them 1013 times will add over 50000 cost units to the basic indexscan.
That part I believe --- correlated subqueries are expensive.
regards, tom lane
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