Re: Slow SELECT with distinct, in a TIMESTAMP type column

When i make the set enable_seqscan = off the result is:

dbname=# set enable_seqscan = off;
SET VARIABLE
dbname=# explain analyze SELECT distinct(smsdate) FROM send_total;

NOTICE:  QUERY PLAN:

Unique  (cost=0.00..31084.39 rows=1232 width=8) (actual
time=108.60..195210.91 rows=6676 loops=1) ->  Index Scan using send_total_smsdate_idx on send_total
(cost=0.00..31053.60 rows=12315 width=8) (actual time=108.59..195145.43
rows=12087 loops=1)
Total runtime: 195226.24 msec




On Mon, 2002-06-24 at 19:36, Stephan Szabo wrote:
>
> On 24 Jun 2002, Marcos Garcia wrote:
>
> > The problem is that my query is too slow when i use distinct:
> >
> > pgsql> explain analyze SELECT distinct(smsdate) FROM send_total;
> >
> > NOTICE:  QUERY PLAN:
> >
> > Unique  (cost=15840.31..15870.81 rows=1220 width=8) (actual
> > time=56358.93..56452.78 rows=6670 loops=1)
> >   ->  Sort  (cost=15840.31..15840.31 rows=12203 width=8) (actual
> > time=56358.91..56436.95 rows=12062 loops=1)
> >         ->  Seq Scan on send_total  (cost=0.00..15012.03 rows=12203
> > width=8) (actual time=0.55..56205.25 rows=12062 loops=1)
> > Total runtime: 56518.26 msec
>
> As a question, what does explain analyze show if you
> set enable_seqscan=off; first?
>
--
M.P.Garcia
PT Inovação, SA
Serviços e Redes Móveis
Rua José Ferreira Pinto Basto - 3810 Aveiro
Tel: 234 403 253  -  Fax: 234 424 160
E-mail: marcos-p-garcia@ptinovacao.pt