Re: Slow indexscan

Mikko Partio wrote:
>
>
> On 6/20/07, *Tom Lane* <tgl@sss.pgh.pa.us <mailto:tgl@sss.pgh.pa.us>> wrote:
>
>     "Mikko Partio" <mpartio@gmail.com <mailto:mpartio@gmail.com>> writes:
>
>      >  Index Scan using tbl_20070601_pkey on tbl_20070601 t1
>      > (cost=0.00..365.13rows=13 width=137) (actual time=
>      > 120.83..10752.64 rows=539 loops=1)
>      >    Index Cond: ((validtime >= 20070602000000::bigint) AND
>     (validtime <=
>      > 20070602235500::bigint) AND (latitude = 60.2744::double
>     precision) AND
>      > (longitude = 26.4417::double precision))
>      >    Filter: (parname = 'temperature'::character varying)
>
>     You do realize that's going to scan the entire index range from
>     20070602000000 to 20070602235500?
>
>     If this is a typical query you'd be better off putting the lat/long
>     columns first in the index.
>
>                             regards, tom lane
>
>
>
> Thanks for the reply.
>
> Adding a new index does not speed up the query (although the planner
> decides to use the index):
>
> db=# create index tbl_20070601_latlonvalidpar_index on tbl_20070601
> (latitude,longitude,validtime,parname);
> CREATE INDEX
>
> db=# explain analyze select * from tbl_20070601 where validtime between
> 20070602000000 and 20070602235500 and latitude= 60.2744 and
> longitude=26.4417 and parname in ('temperature');
>
> QUERY PLAN
>
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

>
>  Index Scan using tbl_20070601_latlonvalidpar_index on tbl_20070601 t1
> (cost=0.00..29.18 rows=13 width=137) (actual time=3471.94..31542.90
> rows=539 loops=1)
>    Index Cond: ((latitude = 60.2744::double precision) AND (longitude =
> 26.4417::double precision) AND (validtime >= 20070602000000::bigint) AND
> (validtime <= 20070602235500::bigint) AND (parname =
> 'temperature'::character varying))
>  Total runtime: 31544.48 msec
> (3 rows)
>
>
> This is a very typical query and therefore it should be made as fast as
> possible. There are several tables like this rowcount ranging from 3
> million to 13 million. I have some possibilities to modify the queries
> as well as the tables, but the actual table structure is hard coded.
>
> Any other suggestions?

Try increasing your default_statistics_target and rerunning explain
analyze. Secondly try increasing your work_mem.

Joshua D. Drake


>
> Regards
>
> MP
>
>


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