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From: Greg Smith <gsmith@gregsmith.com>
To: pgsql-performance@postgresql.org
Subject: Re: New to PostgreSQL, performance considerations
Date: Tue, 12 Dec 2006 11:36:01 -0500 (EST)
Message-ID: <Pine.GSO.4.64.0612121123280.7466@westnet.com> (raw)
In-Reply-To: <20061212161106.GF22782@alvh.no-ip.org>
References: <20061211173105.GH16692@mathom.us>
	<E1Gtplp-0004Ka-GM@elasmtp-junco.atl.sa.earthlink.net>
	<20061211184726.GI16692@mathom.us>
	<E1GtrB8-0005rw-Iu@elasmtp-kukur.atl.sa.earthlink.net>
	<457DA782.3060506@modgraph-usa.com>
	<8a0c7af10612111422x6bdcc0c2p7cbfeb5a7b0e0374@mail.gmail.com>
	<2FC0D8E7-F8ED-452F-BB13-FB665B516E7F@purefiction.net>
	<20061212123252.GR16692@mathom.us>
	<42B14BCF-B745-4F94-B5EA-97997744A4D5@purefiction.net>
	<3356.1165938462@sss.pgh.pa.us>
	<20061212161106.GF22782@alvh.no-ip.org>

On Tue, 12 Dec 2006, Alvaro Herrera wrote:

> While skimming over the pgbench source it has looked to me like it's
> necessary to pass the -s switch (scale factor) to both the
> initialization (-i) and the subsequent (non -i) runs.

For non-custom runs, it's computed based on the number of branches. 
Around line 1415 you should find:

                 res = PQexec(con, "select count(*) from branches");
                 ...
                 scale = atoi(PQgetvalue(res, 0, 0));

So it shouldn't be required during the run, just the initialization.

However, note that there were some recent bug fixes to the scaling 
implementation, and I would recommend using the version that comes with 
8.2 (pgbench 1.58 2006/10/21).  It may compile fine even if you copy that 
pgbench.c into an older version's contrib directory; it's certainly a 
drop-in replacement (and improvement) for the pgbench 1.45 that comes with 
current Postgres 8.1 versions.

--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD



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