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To: postgres@postgres.Berkeley.EDU
Subject: vacuum compaction
Date: Wed, 07 Dec 1994 18:47:55 +0000
From: Giles Nelson <Giles.Nelson@cl.cam.ac.uk>
Message-ID: <"swan.cl.cam.:267290:941207184809"@cl.cam.ac.uk>
Resent-To: postgres-redist@postgres.Berkeley.EDU
Resent-Date: Wed, 07 Dec 94 10:49:56 -0800
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Dear all.

The footnote on page 66 of the POSTGRES manual supplied with V4.2 states
that the vacuum command does not perform any compaction or clustering of data.
The UNIX files therefore never shrink.

POSTGRES does support time travel of course, but this facility can be removed
with the use of "archive=none" specified when creating a class. Tuples in such
a class are accessible after deletion through time travel functions until both
the class is `purge'd and the the database `vacuum'ed. They are then
permanently deleted.

However from the above statement and the size of my database files such tuples
are not actually removed.

This is a problem for me, as I have a rapid update rate. Most queries are in
fact `replaces'.

I could rebuild the database over-night every night to compress it. However
this seems rather nasty.

So, I'm wondering if anyone has managed to get round this problem and actually
been able to permanently remove tuples!

Yours hopefully,

Giles Nelson.

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