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Potential memory usage issue

From: David Brain <dbrain(at)bandwidth(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Subject: Potential memory usage issue
Date: 2007-03-22 12:08:25
Message-ID: 460271B9.8050600@bandwidth.com (view raw or flat)
Thread:
Lists: pgsql-performance
Hi,

I recently migrated one of our large (multi-hundred GB) dbs from an 
Intel 32bit platform (Dell 1650 - running 8.1.3) to a 64bit platform 
(Dell 1950 - running 8.1.5).  However I am not seeing the performance 
gains I would expect - I am suspecting that some of this is due to 
differences I am seeing in reported memory usage.

On the 1650 - a 'typical' postmaster process looks like this in top:

5267 postgres  16   0  439m 427m 386m S  3.0 21.1   3:31.73 postmaster

On the 1940 - a 'typical' postmaster process looks like:

10304 postgres  16   0 41896  13m  11m D    4  0.3   0:11.73 postmaster

I currently have both systems running in parallel so the workloads will 
be approximately equal.  The configurations of the two systems in terms 
of postgresql.conf is pretty much identical between the two systems, I 
did make some changes to logging, but nothing to buffers/shared memory 
config.

I have never seen a postmaster process on the new system consume 
anywhere near as much RAM as the old system - I am wondering if there is 
something up with the shared memory config/usage that is causing my 
performance issues.  Any thoughts as to where I should go from here?

Thanks,

David.


-- 
David Brain - bandwidth.com
dbrain(at)bandwidth(dot)com

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