Re: Tablespaces and query planning

From: "Albe Laurenz" <laurenz(dot)albe(at)wien(dot)gv(dot)at>
To: <cedric(at)2ndquadrant(dot)com>, <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Tablespaces and query planning
Date: 2012-06-11 07:01:24
Message-ID: D960CB61B694CF459DCFB4B0128514C20800ADF1@exadv11.host.magwien.gv.at
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Cédric Villemain wrote:
> > - The statistics gathered by ANALYZE are independent of the tablespace
> > containing the table.
>
> yes.
>
> > - The tablespace containing the table has no influence on query planning
> > unless seq_page_cost or random_page_cost has been set on the
> > tablespace.
>
> yes.
>
> > - VACUUM ANALYZE does the same as VACUUM followed by ANALYZE.
>
> no.
> it is fine grained, but in the diffs there is:
>
> VACUUM and ANALYSE do not update pg_class the same way for the
> reltuples/relpages: for ex VACUUM is accurate for index, and ANALYZE is fuzzy
> so if you issue a vacuum you have exact values, if you then run ANALYZE you
> may change them to be less precise.

Thanks for the confirmationsand the clarification. I hadn't thought of the
statistical entries in pg_class.

Yours,
Laurenz Albe

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