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Message-ID: <4C57FB5D.1020006@gmail.com>
Date: Tue, 03 Aug 2010 13:19:57 +0200
From: Yeb Havinga <yebhavinga@gmail.com>
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To: Hannu Krosing <hannu@2ndquadrant.com>
CC: Scott Marlowe <scott.marlowe@gmail.com>,
	Greg Smith <greg@2ndquadrant.com>,
	Josh Berkus <josh@agliodbs.com>, pgsql-performance@postgresql.org
Subject: Re: Testing Sandforce SSD
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Hannu Krosing wrote:
> Did it fit in shared_buffers, or system cache ?
>   
Database was ~5GB, server has 16GB, shared buffers was set to 1920MB.
> I first noticed this several years ago, when doing a COPY to a large
> table with indexes took noticably longer (2-3 times longer) when the
> indexes were in system cache than when they were in shared_buffers.
>   
I read this as a hint: try increasing shared_buffers. I'll redo the 
pgbench run with increased shared_buffers.
>> so the test is actually how fast the ssd can capture 
>> sequential WAL writes and fsync without barriers, mixed with an 
>> occasional checkpoint with random write IO on another partition). Since 
>> the WAL writing is the same for both block_size setups, I decided to 
>> compare random writes to a file of 5GB with Oracle's Orion tool:
>>     
>
> Are you sure that you are not writing full WAL pages ?
>   
I'm not sure I understand this question.
> Do you have any stats on how much WAL is written for 8kb and 4kb test
> cases ?
>   
Would some iostat -xk 1 for each partition suffice?
> And for other disk i/o during the tests ?
>   
Not existent.

regards,
Yeb Havinga