Re: Planner issue - Mailing list pgsql-performance

This helps a bit when I set it to 1000 - but it's still pretty bad:

I will use an index 220-300, but not 200-300.

Alex

trendmls=# explain analyze select listnum from propmain where
listprice<=300000 and listprice>=200000;
                                                  QUERY PLAN
--------------------------------------------------------------------------------------------------------------
 Seq Scan on propmain  (cost=0.00..15517.56 rows=6842 width=4) (actual
time=0.039..239.760 rows=6847 loops=1)
   Filter: ((listprice <= 300000::numeric) AND (listprice >= 200000::numeric))
 Total runtime: 244.301 ms
(3 rows)

trendmls=# set enable_seqscan=off;
SET
trendmls=# explain analyze select listnum from propmain where
listprice<=300000 and listprice>=200000;
                                                                QUERY PLAN

------------------------------------------------------------------------------------------------------------------------------------------
 Index Scan using propmain_listprice_i on propmain
(cost=0.00..22395.95 rows=6842 width=4) (actual time=0.084..25.751
rows=6847 loops=1)
   Index Cond: ((listprice <= 300000::numeric) AND (listprice >=
200000::numeric))
 Total runtime: 30.193 ms
(3 rows)

trendmls=#



On Tue, 22 Mar 2005 08:22:59 -0800, Joshua D. Drake
<jd@commandprompt.com> wrote:
> Alex Turner wrote:
>
> >I get the following output from explain analyze on a certain subset of
> >a large query I'm doing.
> >
> >
> >
> Try increases the statistics on the listprice column with alter
> table and then re-run analyze.
>
> alter table foo alter column set statistics <n>
>
> Sincerely,
>
> Joshua D. Drake
>
>
> >>From the looks of it, I need to increase how often postgres uses an
> >index over a seq scan, but I'm not sure how to do that.  I looked
> >through the run-time configuration docs on the website, but didn't see
> >anything pertaining to index selectivity.
> >
> >Thanks,
> >
> >Alex Turner
> >netEconomist
> >
> >
> >trendmls=# explain analyze select listnum from propmain where
> >listprice<=300000 and listprice>=220000;
> >                                                  QUERY PLAN
> >--------------------------------------------------------------------------------------------------------------
> > Seq Scan on propmain  (cost=0.00..15556.05 rows=6228 width=4) (actual
> >time=0.093..506.730 rows=5671 loops=1)
> >   Filter: ((listprice <= 300000::numeric) AND (listprice >= 220000::numeric))
> > Total runtime: 510.482 ms
> >(3 rows)
> >
> >trendmls=# explain analyze select listnum from propmain where
> >listprice<=300000 and listprice>=250000;
> >                                                                QUERY PLAN
>
>------------------------------------------------------------------------------------------------------------------------------------------
> > Index Scan using propmain_listprice_i on propmain
> >(cost=0.00..12578.65 rows=3486 width=4) (actual time=0.103..16.418
> >rows=3440 loops=1)
> >   Index Cond: ((listprice <= 300000::numeric) AND (listprice >=
> >250000::numeric))
> > Total runtime: 18.528 ms
> >(3 rows)
> >
> >---------------------------(end of broadcast)---------------------------
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> >
> >
>
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