Speeding up SELECT MAX(),... GROUP BY ... ? - Mailing list pgsql-sql

From Christoph Haller
Subject Speeding up SELECT MAX(),... GROUP BY ... ?
Date
Msg-id 200205221525.RAA26917@rodos
Whole thread Raw
Responses Re: Speeding up SELECT MAX(),... GROUP BY ... ?  (Josh Berkus <josh@agliodbs.com>)
List pgsql-sql
Hi, 

I am having select statements which are running too slow. 
It's PostgreSQL 7.2.1 and a VACUUM ANALYZE was done. 
There are various where clauses restricting the output 
to timepoints and/or ids related to sources,locations,...
One statement looks like: 

EXPLAIN 
select max(timepoint),lid,mid,sid from onfvalue 
where  timepoint <= '2002-05-01 08:00:00'  and  sid in (1,3,5,7)  group by sid,lid,mid; 

NOTICE:  QUERY PLAN:

Aggregate  (cost=21044.07..22383.53 rows=13395 width=20) ->  Group  (cost=21044.07..22048.66 rows=133946 width=20)
->  Sort  (cost=21044.07..21044.07 rows=133946 width=20)             ->  Seq Scan on onfvalue  (cost=0.00..5530.24
rows=133946width=20)
 

Any ideas/alternatives to speed this up? 
The table 'onfvalue' is supposed to keep some million rows. 

Regards, Christoph 


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