Re: Query not using the index

On Tue, Feb 25, 2003 at 07:03:40PM +1100, Mark Halliwell wrote:

> The majority of records (about 6.8 million) have computer = 8 with sequence
> starting at 2200000 and incrementing by 1.
> There are about 497000 records with computer = 3 with the sequence starting at
> 1 and also incrementing by 1.
> There are only a few records with other computer numbers.

> select * from replicate where computer = 3 and sequence >= 490000;
>
> I have created several different indexes (always doing a vacuum analyse
> afterwards etc), but the explain always reports a sequential scan. If I

Try setting the statistics on computer to a much wider value -- say

ALTER TABLE computer ALTER COLUMN computer SET STATISTICS 1000

and see if it helps. You can poke around in the pg_stats view to see
why this might help, and perhaps to get a more realistic idea of what
you need to set the statistics to. The problem is likely the
overwhelming commonality of computer=8.

A

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