From: Steinar H. Gunderson <sgunderson@bigfoot.com>
To: pgsql-performance@postgresql.org
Subject: Re: Why hash join instead of nested loop?
Date: Tue, 9 Aug 2005 03:08:50 +0200
Message-ID: <20050809010850.GA18938@uio.no> (raw)
In-Reply-To: <10930.1123549106@sss.pgh.pa.us>
References: <41b0fe890508051135712a086b@mail.gmail.com>
<001801c59a0a$f4be7480$9a00a8c0@OTTO>
<41b0fe8905080516164464e04f@mail.gmail.com>
<15425.1123304631@sss.pgh.pa.us>
<41b0fe89050808100021a2a4fc@mail.gmail.com>
<10930.1123549106@sss.pgh.pa.us>
On Mon, Aug 08, 2005 at 08:58:26PM -0400, Tom Lane wrote:
> Hmph. There is something really strange going on here. I tried to
> duplicate your problem in 7.4.*, thus:
PostgreSQL 7.4.7 (Debian sarge):
<create table and stuff, exactly the same as you>
regression=# explain analyze select rtmessagestate.* from rtmessagestate,connection where (connection_registry_id = 40105) AND (obj1 = 73582) and id = obj2;
QUERY PLAN
----------------------------------------------------------------------------------------------------------------------------------------------------
Hash Join (cost=4.83..5.91 rows=1 width=14) (actual time=0.155..0.159 rows=1 loops=1)
Hash Cond: ("outer".id = "inner".obj2)
-> Seq Scan on rtmessagestate (cost=0.00..1.05 rows=5 width=14) (actual time=0.003..0.006 rows=5 loops=1)
-> Hash (cost=4.83..4.83 rows=1 width=4) (actual time=0.026..0.026 rows=0 loops=1)
-> Index Scan using connection_regid_obj1_index on connection (cost=0.00..4.83 rows=1 width=4) (actual time=0.011..0.012 rows=1 loops=1)
Index Cond: ((connection_registry_id = 40105) AND (obj1 = 73582))
Total runtime: 0.215 ms
(7 rows)
This is an Opteron (in 32-bit mode), though.
/* Steinar */
--
Homepage: http://www.sesse.net/
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To: pgsql-performance@postgresql.org
Cc: sgunderson@bigfoot.com
Subject: Re: Why hash join instead of nested loop?
In-Reply-To: <20050809010850.GA18938@uio.no>
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