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Re: testing HS/SR - 1 vs 2 performance

From: Stefan Kaltenbrunner <stefan(at)kaltenbrunner(dot)cc>
To: Erik Rijkers <er(at)xs4all(dot)nl>
Cc: Simon Riggs <simon(at)2ndQuadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: testing HS/SR - 1 vs 2 performance
Date: 2010-05-04 19:34:53
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Lists: pgsql-hackers
Erik Rijkers wrote:
> Hi Simon,
> In another thread you mentioned you were lacking information from me:
> On Tue, May 4, 2010 17:10, Simon Riggs wrote:
>> There is no evidence that Erik's strange performance has anything to do
>> with HS; it hasn't been seen elsewhere and he didn't respond to
>> questions about the test setup to provide background. The profile didn't
>> fit any software problem I can see.
> I'm sorry if I missed requests for things that where not already mentioned.
> Let me repeat:
>   OS: Centos 5.4
>   2 quadcores: Intel(R) Xeon(R) CPU X5482 @ 3.20GHz
>   Areca 1280ML
>   primary and standby db both on a 12 disk array (sata 7200rpm, Seagat Barracuda ES.2)
> It goes without saying (I hope) that apart from the pgbench tests
> and a few ssh sessions (myself), the machine was idle.
> It would be interesting if anyone repeated these simple tests and produced
> evidence that these non-HS.
> (Unfortunately, I have at the moment not much time for more testing)

FWIW - I'm seeing a behaviour here under pgbench -S workloads that looks 
kinda related.

using -j 16 -c 16 -T 120 I get either 100000tps and around 660000 
contextswitches per second or on some runs I end up with 150000tps and 
around 1M contextswitches/s sustained. I mostly get the 100k result but 
once in a while I get the 150k one. And one even can anticipate the 
final transaction rate from watching "vmstat 1"...

I'm not sure yet on what is causing that behaviour but that is with 
9.0B1 on a Dual Quadcore Nehalem box with 16 cpu threads (8+HT) on a 
pure in-memory workload (scale = 20 with 48GB RAM).


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