Re: Oracle v. Postgres 9.0 query performance - Mailing list pgsql-performance

From Tony Capobianco
Subject Re: Oracle v. Postgres 9.0 query performance
Date
Msg-id 1307547634.1990.26.camel@tony1.localdomain
Whole thread Raw
In response to Re: Oracle v. Postgres 9.0 query performance  (Tom Lane <tgl@sss.pgh.pa.us>)
Responses Re: Oracle v. Postgres 9.0 query performance  (Stephen Frost <sfrost@snowman.net>)
Re: Oracle v. Postgres 9.0 query performance  (Vitalii Tymchyshyn <tivv00@gmail.com>)
List pgsql-performance
pg_dw=# set enable_nestloop =0;
SET
Time: 0.165 ms
pg_dw=# explain CREATE TABLE ecr_opens with (FILLFACTOR=100)
pg_dw-# as
pg_dw-# select o.emailcampaignid, count(memberid) opencnt
pg_dw-#   from openactivity o,ecr_sents s
pg_dw-#  where s.emailcampaignid = o.emailcampaignid
pg_dw-#  group by o.emailcampaignid;
                                       QUERY
PLAN
-----------------------------------------------------------------------------------------
 HashAggregate  (cost=4391163.81..4391288.05 rows=9939 width=12)
   ->  Hash Join  (cost=14.78..4344767.23 rows=9279316 width=12)
         Hash Cond: (o.emailcampaignid = s.emailcampaignid)
         ->  Seq Scan on openactivity o  (cost=0.00..3529930.67
rows=192540967 width=12)
         ->  Hash  (cost=8.79..8.79 rows=479 width=4)
               ->  Seq Scan on ecr_sents s  (cost=0.00..8.79 rows=479
width=4)

Yikes.  Two sequential scans.


On Wed, 2011-06-08 at 11:33 -0400, Tom Lane wrote:
> Tony Capobianco <tcapobianco@prospectiv.com> writes:
> > pg_dw=# explain CREATE TABLE ecr_opens with (FILLFACTOR=100)
> > pg_dw-# as
> > pg_dw-# select o.emailcampaignid, count(memberid) opencnt
> > pg_dw-#   from openactivity o,ecr_sents s
> > pg_dw-#  where s.emailcampaignid = o.emailcampaignid
> > pg_dw-#  group by o.emailcampaignid;
> >                                                  QUERY
> > PLAN
> > -------------------------------------------------------------------------------------------------------------
> >  GroupAggregate  (cost=0.00..1788988.05 rows=9939 width=12)
> >    ->  Nested Loop  (cost=0.00..1742467.24 rows=9279316 width=12)
> >          ->  Index Scan using ecr_sents_ecid_idx on ecr_sents s
> > (cost=0.00..38.59 rows=479 width=4)
> >          ->  Index Scan using openact_emcamp_idx on openactivity o
> > (cost=0.00..3395.49 rows=19372 width=12)
> >                Index Cond: (o.emailcampaignid = s.emailcampaignid)
> > (5 rows)
>
> > Should this query be hashing the smaller table on Postgres rather than
> > using nested loops?
>
> Yeah, seems like it.  Just for testing purposes, do "set enable_nestloop
> = 0" and see what plan you get then.
>
>             regards, tom lane
>



pgsql-performance by date:

Previous
From: Tom Lane
Date:
Subject: Re: Oracle v. Postgres 9.0 query performance
Next
From: Stephen Frost
Date:
Subject: Re: Oracle v. Postgres 9.0 query performance