Re: index use again and again

On Tue, 12 Feb 2002, Roderick A. Anderson wrote:

> On Tue, 12 Feb 2002, Holger Marzen wrote:
>
> > I read the Postgres boog, browsed the mailing list archives and have
> > still no clue.
> >
> > I have a table with about 150.000 rows and put some indexes (not unique)
> > on it. If I use "=" in the where clause tha index is used, if I use ">"
> > or "between" then it is not used. It happens both with 7.1.3 and the new
> > 7.2:
>
> Previous discussion on this topic give me the idea that index use is
> determined by the optimizer and it will use and index or sequential
> depending on some percentage of the records it thinks will be returned.
>    I.e. is it more economical to just go through them all or spend time
> jumping around getting the right records.  Of course one of the hackers
> will be able to give you a much better and probably correct explanation.

Yes. When I choose a ">" that returns only a few rows then EXPLAIN
reports an index scan. So it's depending on the number of returned rows.

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