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From: Paul Brunner <brunner@gdc.com>
To: postgres@postgres.Berkeley.EDU
Cc: brunner@gdc.com
Subject: vacuum command functions
Date: Fri, 8 Jul 94 12:34:09 EDT
Message-ID: <9407081634.AA17138@mailhost.gdc.com> (raw)

In the 4.2 release of POSTGRES from Berkeley, there is a vacuum command,
one of whose stated purposes is to update statistics on the database used by
the query optimizer to select the best execution plan.

I was reading a paper comparing university POSTGRES with the database system
produced by Illustra Software, Inc. (a commercialization of the POSTGRES
research software.) In the paper, it states that the POSTGRES vacuum command
never actually updates these statistics. Tests I've run show the attributes
of "relpages" and "reltuples" being updated by running the vacuum after
appending rows to classes.

Does the vacuum command indeed update the statistics to reflect the current 
state of the database, regardless of whatever kind of alterations have been
made to the data?


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