Re: too low cost of Bitmap index scan

2016-12-20 13:55 GMT+01:00 Robert Haas <robertmhaas(at)gmail(dot)com>:

> On Tue, Dec 20, 2016 at 2:13 AM, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
> wrote:
> > 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?
>
> Hmm, seems like you'd be paying the operator cost either way. No?
>

It looks so this cost is much more significant in index scan feature

Pavel

>
> --
> Robert Haas
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