From: Bruce Momjian <pgman@candle.pha.pa.us>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Jeff Self <jself@nngov.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: SQL performance issue with PostgreSQL compared to MySQL
Date: Wed, 19 Jun 2002 12:43:04 -0400 (EDT)
Message-ID: <200206191643.g5JGh4D10793@candle.pha.pa.us> (raw)
In-Reply-To: <4193.1024496331@sss.pgh.pa.us>
Tom Lane wrote:
> Jeff Self <jself@nngov.com> writes:
> > if it's too OT, let me know, and I'll stop. The query "SELECT authuser,
> > SUM(bytes) AS traffic FROM logfile GROUP BY authuser ORDER BY traffic"
> > [is slow]
>
> What datatype are the columns used in the query? And what PG version
> are we talking about?
My guess is that is the lack of hashing for GROUP BY aggregating that is
killing us. TODO has:
* Add hash for evaluating GROUP BY aggregates
and I specifically remember MySQL has such a hash. The big question is
how many unique values are there in the group. If it is large, the
missing hashing could be the problem.
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
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To: pgsql-sql@postgresql.org
Cc: pgman@candle.pha.pa.us, tgl@sss.pgh.pa.us, jself@nngov.com
Subject: Re: SQL performance issue with PostgreSQL compared to MySQL
In-Reply-To: <200206191643.g5JGh4D10793@candle.pha.pa.us>
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