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Re: pg9.0.3 explain analyze running very slow compared to a different box with much less configuration

From: "Strange, John W" <john(dot)w(dot)strange(at)jpmchase(dot)com>
To: Marti Raudsepp <marti(at)juffo(dot)org>, DM <dm(dot)aeqa(at)gmail(dot)com>
Cc: Achilleas Mantzios <achill(at)matrix(dot)gatewaynet(dot)com>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: pg9.0.3 explain analyze running very slow compared to a different box with much less configuration
Date: 2011-03-25 14:25:45
Message-ID: EF37296944B47C40ADDCCB7BFD6289FE04942C323E@EMASC201VS01.exchad.jpmchase.net (view raw or flat)
Thread:
Lists: pgsql-performance
If it's a HP box you can also turn this off via the bios via your RBSU:

Starting with HP ProLiant G6 servers that utilize Intel® Xeon® processors, setting the HP Power Profile 
Option in RBSU to Maximum Performance Mode sets these recommended additional low-latency options 
for minimum BIOS latenc


-----Original Message-----
From: pgsql-performance-owner(at)postgresql(dot)org [mailto:pgsql-performance-owner(at)postgresql(dot)org] On Behalf Of Marti Raudsepp
Sent: Friday, March 25, 2011 3:30 AM
To: DM
Cc: Achilleas Mantzios; pgsql-performance(at)postgresql(dot)org
Subject: Re: [PERFORM] pg9.0.3 explain analyze running very slow compared to a different box with much less configuration

2011/3/25 DM <dm(dot)aeqa(at)gmail(dot)com>:
> gettimeofday() on my new box is slow, after further research we found 
> that, when we set ACPI=Off, we got a good clock performance even the 
> explain analyze gave approximately gave the right values, but the 
> hyperthreading is off.

Disabling ACPI also disables most CPU power management, so that explains why you get a stable TSC that way. But that's not a real fix.

> could you guide me how to set, the parameter current_clocksource to 
> TSC,

You can't "set" it, the kernel will automatically choose TSC, if it's stable, at boot time; see messages in dmesg.

A better way to disable power management on CentOS is to disable the 'cpuspeed' service.

Note that this is not necessary for newer CPUs; Intel Nehalem and AMD Phenom series have a stable TSC even with power management enabled.

Regards,
Marti

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