Re: bitmap-index-scan slower than normal index scan

Tom Lane <tgl@sss.pgh.pa.us> schrieb:


Thanks you and Alex for the response.

> > PostgreSQL 8.1.4 on i386-pc-linux-gnu, compiled by GCC cc (GCC) 3.3.5 (Debian 1:3.3.5-13)
>
> You need a newer one.

I know ;-)

>
> This is simply a stupid choice on the part of choose_bitmap_and() ---
> it's adding on a second index to try to filter on maschine when that
> scan will actually just increase the cost.
>
> I've revisited choose_bitmap_and() a couple times since then; try
> 8.1.9 and see if it gets this right.

Okay, but later.

>
> Also, part of the problem here looks to be an overestimate of the number
> of rows matching ab = 347735.  It might help to increase the statistics
> target for that column.

I will try this tomorrow and inform you about the result. I've never
done this before, i need to read the docs about this.

Thank you again.


Andreas
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