From: | Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> |
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To: | Greg Smith <greg(at)2ndquadrant(dot)com> |
Cc: | felix <crucialfelix(at)gmail(dot)com>, sthomas(at)peak6(dot)com, pgsql-performance(at)postgresql(dot)org |
Subject: | Re: Really really slow select count(*) |
Date: | 2011-02-04 19:01:08 |
Message-ID: | AANLkTi=NAyNcmhMX5J3X5q2R7KgAO1XkTX=Afue_XZaN@mail.gmail.com |
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Lists: | pgsql-performance |
On Fri, Feb 4, 2011 at 11:38 AM, Greg Smith <greg(at)2ndquadrant(dot)com> wrote:
> You don't turn it on; it's a one time operation that does a cleanup. It is
> by far the easiest way to clean up the mess you have right now. Moving
> forward, if you have max_fsm_pages set to an appropriate number, you
> shouldn't end up back in this position again. But VACUUM along won't get
> you out of there, and VACUUM FULL is always a worse way to clean this up
> than CLUSTER.
note that for large, randomly ordered tables, cluster can be pretty
slow, and you might want to do the old:
begin;
select * into temporaryholdingtable order by somefield;
truncate oldtable;
insert into oldtables select * from temporaryholdingtable;
commit;
for fastest performance. I've had Cluster take hours to do that the
above does in 1/4th the time.
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