Re: Queries not using Index

On Tue, 23 Jul 2002, Daryl Herzmann wrote:

>
> >On Tue, 23 Jul 2002, Daryl Herzmann wrote:
> >
> >> snet=# explain analyze select * from t2002_06 WHERE station = 'SAMI4';
> >> NOTICE: QUERY PLAN:
> >>
> >> Seq Scan on t2002_06 (cost=0.00..35379.69 rows=34979 width=47) (actual
> >> time=67.89..3734.93 rows=38146 loops=1)
> >> Total runtime: 3748.33 msec
> >>
> >> EXPLAIN
> >>
> >> snet=# set enable_seqscan=off;
> >> SET VARIABLE
> >> snet=# explain analyze select * from t2002_06 WHERE station = 'SAMI4';
> >> NOTICE: QUERY PLAN:
> >>
> >> Index Scan using t2002_06_station_idx on t2002_06 (cost=0.00..132124.96
> >> rows=34979 width=47) (actual time=72.03..298.85 rows=38146 loops=1)
> >> Total runtime: 317.76 msec
> >
> >Looks like the estimated cost is way divorced from reality. Is the
> >34979 row estimate even realistic and how well ordered is the table
> >(actually output from pg_statistic would be good as well :) ).
>
> Thanks for the help! I am not sure if I can answer your questions. I will
> try :)
>
> I believe the row estimate is realistic based on this value.
>
> snet=# select count(*) from t2002_06 WHERE station = 'SAMI4';
> count
> -------
> 38146

> I am really sorry, but I don't know what to output from pg_statistic. I
> searched around on the Internet and was not sure what to send you from
> this table. Sorry :(

Right... sorry about that...
select * from pg_statistic where starelid=(select oid from pg_class
where relname='t2002_06';