huge difference in TPS depending of synchornous_commit setting

From: Sergey Kirillov <sergey(dot)kirillov(at)gmail(dot)com>
To: pgsql-novice(at)postgresql(dot)org
Subject: huge difference in TPS depending of synchornous_commit setting
Date: 2012-08-09 06:44:34
Message-ID: CAJjUSnD8YJn3H3UP6tPLWaqntOgZbW-AV_qPhNi6gr8d8XNgYA@mail.gmail.com
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Hi.

I'm having problems with PostgreSQL performance.

My server has good CPU and lots of memory, but just two SATA 7200 hard
drives in software RAID1.

When running pgbench I'm getting 68 TPS with synchronous_commit turned on,
and 3100 TPS with synchronous commit turned off.

Can somebody tell me why there is such big difference? Is it normal to have
it like this?

PS: During run of pgbench with synchronous commit on system is mostly idle,
iowait is 0.12%

--
Best regards,
Sergey

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