Re: [SQL] [PERFORM] 7.3.1 index use / performance

On Tue, 7 Jan 2003, Tom Lane wrote:

> Rod Taylor <rbt(at)rbt(dot)ca> writes:
> >> I am wondering about a compiler bug, or some other peculiarity on your
> >> platform. Can anyone else using FreeBSD try the above experiment and
> >> see if they get different results from mine on 7.3.* (or CVS tip)?
>
> > On FreeBSD 4.7 I received the exact same results as Tom using the
> > statements shown by Tom.
>
> On looking at the code, I do see part of a possible mechanism for this
> behavior: cost_index calculates the estimated cost for qual-clause
> evaluation like this:
>

This bizarre index decreased cost (when adding conditions) behaviour maybe
was due to some vacuums.
(i cant remember how many reloads and vacuums i did to the database
in the period petween the two emails).

However my linux machine with the same pgsql 7.3.1, with a full clean
installation also gives the same symptoms:
Choosing the slow index, and after some (random)
vacuums choosing the right index, and then after some vacuums chooses the
bad
index again.

>
> regards, tom lane
>

==================================================================
Achilleus Mantzios
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IT dept
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