Message-ID: <519F5B4B.5010101@2ndQuadrant.com>
Date: Fri, 24 May 2013 08:21:31 -0400
From: Greg Smith <greg@2ndQuadrant.com>
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Subject: Re: pgbench: spike in pgbench results(graphs) while testing
	pg_hint_plan performance
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On 5/23/13 7:39 AM, Sachin D. Bhosale-Kotwal wrote:
> So i am not getting why spike occure at *12:09:14 *only*.*

This could easily be caused by something outside of the test itself. 
Background processes.  A monitoring system kicking in to write some data 
to disk will cause a drop like this.

Three things you could look into to try and track down the issue:

-Did you turn on log_checkpoints to see if one happens to run when the 
rate drops?  If so, that could be the explanation.  Looks like you setup 
the test to make this less likely, but checkpoints are tough to 
eliminate altogether.

-Does this happen on every test run?  Is it at the same time?

-You can run "top -bc" to dump snapshots of what the system is doing 
every second.  With some work you can then figure out what was actually 
happening during the two seconds around when the throughput dropped.

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


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