To: Tony Capobianco <tcapobianco@prospectiv.com>
cc: pgsql-performance@postgresql.org
Subject: Re: Oracle v. Postgres 9.0 query performance 
In-reply-to: <1307545892.1990.23.camel@tony1.localdomain> 
References: <1307545892.1990.23.camel@tony1.localdomain>
Comments: In-reply-to Tony Capobianco <tcapobianco@prospectiv.com>
	message dated "Wed, 08 Jun 2011 11:11:32 -0400"
Date: Wed, 08 Jun 2011 11:33:05 -0400
Message-ID: <10260.1307547185@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

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