Re: Configuration Optimisation

On 1/14/2010 7:31 AM, Howard Cole wrote:
> Hi,
>
> I am trying to optimise a database server to give the best performance
> possible, so I switched from windows 2k3 to linux (ubuntu 9.10) on the
> basis that most people seem to be of the opinion that postgres runs
> better on linux than windows. To test my optimisation of the system, I
> run a simple pgbench setup for 2 minutes. Not very scientific I realise
> but it has helped me tune systems quite well in the past.
>
> My problem is that I am getting nowhere near the performance of windows
> on my linux build.
>
> For example,
>
> Test setup: pgbench -i -s 5
> Test run: pgbench -T 120
>
> You may think this is a short test, but running it for much longer does
> not seem to make a significant difference.
>
> Now running on windows I get ~ 700 TPS, but on linux I am getting ~70 TPS.
>
> The hardware configuration is Dual Opteron, 8GB Ram and 4 sata disks in
> a Hardware Raid 10 configuration.
>
> There is a change in hardware configuration, from Raid5 on the Windows
> system - But I would expect that switching to raid 10 would give a
> performance boost.
>
> Here are some of the changed settings in my liunx configuration:
>
> shared_buffers = 1900MB
> work_mem = 50MB
> checkpoint_segments = 32
>
> Am I missing something obvious - or is it a waste of time using the
> pgbench as a judge of optimisation in these circumstances?
>
> Thanks.
>
> Howard Cole
> www.selestial.com
>
>

I think an important question is: are both os's really flushing all the
way to disk, or is someone lying to you?

Assuming your workload is IO bound, I'd bet windows is write caching and
linux is not.

Did you try a dd test on linux?

This is a HW Raid, are there any params you can set for
caching/writeback/etc? Do you know what the windows settings were?

-Andy