Message-ID: <4E40AF07.9050004@2ndquadrant.com>
Date: Mon, 08 Aug 2011 23:52:39 -0400
From: Greg Smith <greg@2ndquadrant.com>
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To: Dusan Misic <promisic@gmail.com>
CC: pgsql-performance@postgresql.org
Subject: Re: Postgres performance on Linux and Windows
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Dusan Misic wrote:
>
> I had done some testing for my application (WIP) and I had executed 
> same SQL script and queries on real physical 64-bit Windows 7 and on 
> virtualized 64-bit CentOS 6.
>
> Both database servers are tuned with real having 8 GB RAM and 4 cores, 
> virtualized having 2 GB RAM and 2 virtual cores.
>
> Virtualized server crushed real physical server in performance in both 
> DDL and DML scripts.
>
> My question is simple. Does PostgreSQL perform better on Linux than on 
> Windows and how much is it faster in your tests?
>

You didn't mention what tuning you did on the Windows server.  If you 
set shared_buffers to a large value, more than around 512MB, that's been 
reported to slow the server down rather than make it faster on that OS.

The other thing you can easily get wrong in this sort of comparison is 
having one server enforce synchronous writes, while the other cheats.  
Many virtualized systems will not flush information to disk properly 
during writes, which is faster but can lead to database corruption after 
a crash.  See http://wiki.postgresql.org/wiki/Reliable_Writes for more 
information on this general topic.  Generally for a VM solution, you 
need to check if it properly handles the "fsync" system call.

Comparing performance across two different operating systems fairly is 
really hard to get right.  It's easy to skew the results because of 
something unrelated to the difference in database performance, such as 
Kevin's commentary about network speed heavily influencing results.

-- 
Greg Smith   2ndQuadrant US    greg@2ndQuadrant.com   Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support  www.2ndQuadrant.us