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Re: Flush Shared Buffer Cache

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: "Chander Ganesan" <chander(at)otg-nc(dot)com>, <pgsql-admin(at)postgresql(dot)org>, "Suvankar Roy" <suvankar(dot)roy(at)tcs(dot)com>
Subject: Re: Flush Shared Buffer Cache
Date: 2009-07-16 21:07:09
Message-ID: 4A5F502D020000250002888B@gw.wicourts.gov (view raw or flat)
Thread:
Lists: pgsql-admin
Suvankar Roy <suvankar(dot)roy(at)tcs(dot)com> wrote:
 
> Actually I am trying to figure out how much execution time any query
> is taking is taking when executed for the first time.
> 
> Because once a query is executed for the first time, the query plan,
> data buffer is cached so subsequently time taken is much lower.
> 
> For this, I want to have the Shared buffer cache flushed to note
> the initial execution time.
> 
> Is my understanding correct here ?
 
Keep in mind that the OS cache will also normally have a significant
amount of PostgreSQL data cached.  For "uncached" timings, you will
need to purge this, too.  Of course, for real-life production
benchmarks the most meaningful timings are normally those taken within
your actual production mix, with all the caching and resource
competition which goes along with that.
 
-Kevin

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