From: Tom Lane <tgl@sss.pgh.pa.us>
To: John A Meinel <john@arbash-meinel.com>
Cc: Edin Kadribasic <edink@emini.dk>
Cc: pgsql-performance@postgresql.org
Subject: Re: Optimizer wrongly picks Nested Loop Left Join
Date: Wed, 11 May 2005 11:03:43 -0400
Message-ID: <4085.1115823823@sss.pgh.pa.us> (raw)
In-Reply-To: <428210FF.4090302@arbash-meinel.com>
References: <001f01c55604$494d2e60$1200000a@intra.emini.dk>
<428210FF.4090302@arbash-meinel.com>
John A Meinel <john@arbash-meinel.com> writes:
> Unfortunately, because Hash Join doesn't report the number of rows
> (rows=0 always), it's hard to tell how good the estimator is.
This is only a cosmetic problem because you can just look at the number
of rows actually emitted by the Hash node's child; that's always exactly
the number loaded into the hashtable.
(But having said that, it is fixed in CVS tip.)
You may be confused though --- the Hash node is not the Hash Join node.
A zero report from Hash Join does actually mean that it emitted zero
rows.
regards, tom lane
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, john@arbash-meinel.com, edink@emini.dk
Subject: Re: Optimizer wrongly picks Nested Loop Left Join
In-Reply-To: <4085.1115823823@sss.pgh.pa.us>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox