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Re: Bug? 8.0 does not use partial index

From: Palle Girgensohn <girgen(at)pingpong(dot)net>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: John Hansen <john(at)geeknet(dot)com(dot)au>, pgsql-hackers(at)postgreSQL(dot)org
Subject: Re: Bug? 8.0 does not use partial index
Date: 2005-01-14 00:52:04
Message-ID: 3D561B2C03CA093DAB3BBA5B@palle.girgensohn.se (view raw or flat)
Thread:
Lists: pgsql-hackers

--On torsdag, januari 13, 2005 19.44.57 -0500 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> 
wrote:

> Palle Girgensohn <girgen(at)pingpong(dot)net> writes:
>> Trying all this out, I realize that on 7.4.5, I can sometimes get
>> different  results after `vacuum analyze' vs. a plain `analyze' (again,
>> not exactly  the same data, and I cannot reproduce this on the other
>> machine with the  data I sent you). It does not really relate to the
>> question above, but  perhaps you can explain how come I get different
>> results?
>
> No surprise.  vacuum analyze produces an exact total row count, whereas
> analyze can only produce an approximate total row count (since it only
> samples the table rather than groveling over every row).  Sometimes the
> approximate count will be far enough off to affect the estimates.

Reasonable. Thanks for clarifying that. In the normal case, vacuum analyze 
is better, I guess?

/Palle

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