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Date: Mon, 9 Mar 2009 17:43:52 +0100
From: Nicolas Haller <nicolas@boiteameuh.org>
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Subject: Re: Busy disk and page fault
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On Mon, Mar 09, 2009 at 05:04:16PM +0100, Wojciech Puchar wrote:
>> The server is overload, the disk is 100% busy with 250 write operations
>> per second and a throuput of 6MB/s.
>> My first idea is because of mass random access/write on the disk. But I also see
>> the server can make 20k page fault per second.

> what page fault? most page faults in FreeBSD doesn't mean disk access,  
> just no mapping present in page tables, which gets mapped after the 
> fault.

> Only if page is actually not present in memory it is fetched from disk.

> top shows in what state is a process.
> if it's biord or biorw - it's doing disk/file I/O, not swapping.

The box don't swap. I just ask if page fault interrupt postgresql
process and fragment/de-optimize disk write.

-- 
Nicolas Haller