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From: Chris Browne <cbbrowne@acm.org>
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Subject: Re: Does VACUUM reorder tables on clustered indices
Date: Wed, 21 Dec 2005 18:36:45 -0500
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jnasby@pervasive.com ("Jim C. Nasby") writes:
> On Wed, Dec 21, 2005 at 12:34:12AM +0100, ipv@tinet.org wrote:
>> Hi,
>> 
>> Utilize <b>CLUSTER;</b> (after vacuum) to reorder the data.
>
> Why would you vacuum when cluster is just going to wipe out the dead
> tuples anyway?

There is one reason to VACUUM before running CLUSTER...

That is that VACUUM will be *guaranteed* to draw all the pages into memory.

Subsequently, you can be certain that the pages are in cache, and that
the CLUSTER should need to do minimal I/O to read data into memory.

If I'm considering clustering the Slony-I "sl_log_1" table, forcing it
into memory *is* something I'll consider doing in order to minimize
the time that would-be writers are blocked from writing...
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