Re: too low cost of Bitmap index scan

2016-12-19 23:28 GMT+01:00 Robert Haas <robertmhaas(at)gmail(dot)com>:

> On Sat, Dec 17, 2016 at 3:30 AM, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
> wrote:
> > -> Bitmap Heap Scan on "Zasilka" (cost=5097.39..5670.64 rows=1
> width=12)
> > (actual time=62.253..62.400 rows=3 loops=231)
> ...
> > When I disable bitmap scan, then the query is 6x time faster
> ....
> > -> Index Scan using "Zasilka_idx_Dopravce" on "Zasilka"
> > (cost=0.00..30489.04 rows=1 width=12) (actual time=15.651..17.187 rows=3
> > loops=231)
> > Index Cond: ("Dopravce" = "Dopravce_Ridic_1"."ID")
> > Filter: (("StavDatum" > (now() - '10 days'::interval)) AND
> (("Stav" =
> > 34) OR ("Stav" = 29) OR ("Stav" = 180) OR ("Stav" = 213) OR ("Stav" =
> 46) OR
> > (("Produkt" = 33) AND ("Stav" = 179)) OR ((("ZpetnaZasilka" =
> '-1'::integer)
> > OR ("PrimaZasilka" = '-1'::integer)) AND ("Stav" = 40))))
> > Rows Removed by Filter: 7596
>
> I'm not sure, but my guess would be that the query planner isn't
> getting a very accurate selectivity estimate for that giant filter
> condition, and that's why the cost estimate is off.
>

maybe operator cost is too high?

Regards

Pavel

> --
> Robert Haas
> EnterpriseDB: http://www.enterprisedb.com
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