From: Tom Lane <tgl@sss.pgh.pa.us>
To: Greg Smith <gsmith@gregsmith.com>
Cc: Gauri Kanekar <meetgaurikanekar@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Replication Syatem
Date: Tue, 29 Apr 2008 10:16:02 -0400
Message-ID: <873.1209478562@sss.pgh.pa.us> (raw)
In-Reply-To: <Pine.GSO.4.64.0804290347560.20575@westnet.com>
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<20080428162243.GN2970@commandprompt.com>
<7e4ba9550804282246p73c62fc6y5e7cb7dda55a6b50@mail.gmail.com>
<Pine.GSO.4.64.0804290347560.20575@westnet.com>
Greg Smith <gsmith@gregsmith.com> writes:
> The model here assumes that you'll need that space again for the next time
> you UPDATE or INSERT a row. So instead VACUUM just keeps those available
> for database reuse rather than returning it to the operating system.
> Now, if you don't VACUUM frequently enough, this model breaks down, and
> the table can get bigger with space that may never get reused. The idea
> is that you should be VACUUMing up now unneeded rows at about the same
> rate they're being re-used. When you don't keep up, the database can
> expand in space that you don't get back again. The right answer to this
> problem is not to use VACUUM FULL; it's to use regular VACUUM more often.
Also, you need to make sure you have the FSM parameters set high enough
so that all the free space found by a VACUUM run can be remembered.
The less often you run VACUUM, the more FSM space you need, because
there'll be more free space reclaimed per run.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, gsmith@gregsmith.com, meetgaurikanekar@gmail.com
Subject: Re: Replication Syatem
In-Reply-To: <873.1209478562@sss.pgh.pa.us>
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