Re: BUG #8326: pgbench tps wrong BUG

From: Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>
To: digoal(at)126(dot)com
Cc: PostgreSQL Bugs List <pgsql-bugs(at)postgresql(dot)org>
Subject: Re: BUG #8326: pgbench tps wrong BUG
Date: 2013-07-26 07:17:17
Message-ID: alpine.DEB.2.02.1307260857150.4397@localhost6.localdomain6
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> when client thread big, the tps without connection time wrong!!!!
> number of threads: 100
> duration: 10 s

My 0.02 €:

I cannot test that on my laptop! What kind of server is this?

The thread start time is currently taken before thread creation. The
overhead of creating 100 threads compared to 10 seconds of run is quite
significant and may impact the result. The second issue is that 800
connections and as many server processes must be created, and the time for
that must be quite significant as well against the 10 second run.

So I would mostly classify that as a feature rather than a bug, because
the run is so short.

BTW, I'm planning to submit an enhancement patch to pgbench to improve
measurements, that will include moving the start time after the thread is
started, and possibly help getting more consistent figures.

--
Fabien.

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