Message-ID: <51352445.4050305@2ndQuadrant.com>
Date: Mon, 04 Mar 2013 17:46:29 -0500
From: Greg Smith <greg@2ndQuadrant.com>
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To: Costin Oproiu <costin.oproiu@gmail.com>
CC: pgsql-performance@postgresql.org
Subject: Re: pgbench intriguing results: better tps figures for
	larger scale factor
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On 2/26/13 4:45 PM, Costin Oproiu wrote:
> First, I've got no good explanation for this and it would be nice to
> have one. As far as I can understand this issue, the heaviest update
> traffic should be on the branches table and should affect all tests.

 From http://www.postgresql.org/docs/current/static/pgbench.html :

"For the default TPC-B-like test scenario, the initialization scale 
factor (-s) should be at least as large as the largest number of clients 
you intend to test (-c); else you'll mostly be measuring update 
contention. There are only -s rows in the pgbench_branches table, and 
every transaction wants to update one of them, so -c values in excess of 
-s will undoubtedly result in lots of transactions blocked waiting for 
other transactions."

I normally see peak TPS at a scale of around 100 on current generation 
hardware, stuff in the 4 to 24 core range.  Nowadays there really is no 
reason to consider running pgbench on a system with a smaller scale than 
that.  I normally get a rough idea of things by running with scales 100, 
250, 500, 1000, 2000.

-- 
Greg Smith   2ndQuadrant US    greg@2ndQuadrant.com   Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support www.2ndQuadrant.com


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