Re: New VACUUM FULL

From: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
To: Simon Riggs <simon(at)2ndQuadrant(dot)com>
Cc: Takahiro Itagaki <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: New VACUUM FULL
Date: 2010-01-30 14:38:31
Message-ID: 4B644467.8080506@enterprisedb.com
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Simon Riggs wrote:
> On Wed, 2010-01-06 at 14:41 +0900, Takahiro Itagaki wrote:
>
>> I just applied the patch with a few additional comments.
>
> I just realised that this new feature *removes* any clustering that was
> previously defined on a table.

Hmm, that's an overstatement. If the table was in order before, it will
be in the same order after VACUUM FULL, all empty gaps and dead tuples
are just removed. It also doesn't clear the indisclustered field in
pg_index, so the next time you run CLUSTER it will cluster the table
just fine.

I'm guessing that you mean that VACUUM FULL doesn't reorder the table
like CLUSTER does. I think that's OK, it has never done that. In fact
the current situation is already an improvement, the new VACUUM FULL
doesn't reshuffle the table and destroy old ordering like the old one does.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com

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