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From David kerber <dcker...@verizon.net>
Subject Re: Performance with many small requests
Date Fri, 08 May 2009 14:00:19 GMT
Peter Crowther wrote:
>> From: David kerber [mailto:dckerber@verizon.net]
>> Also, right now I'm doing a .flush() after the .write() to the log
>> file.  Is that usually necessary, other than to avoid losing
>> data lines in case of a system failure?
>>     
>
> No, other than that.
>
> What disk subsystem are you running on?  Start Performance Monitor and, from Physical
Disks, monitor your disk writes per second.  If it's over 150(ish, depending on the disk)
per spindle in your disk array, you're saturating your disks.
>   
I don't recall the exact disk configuration, but it's pretty robust and 
on par with the rest of the system, because this server was originally 
spec'd as a combination file and application server. 

>   
>> How would a
>> .flush() affect the speed of returning from a synchronized .write()?
>>     
>
> It can be significant, as the data has to get to the file.  I'd check the above.  Also,
do you have any battery-backed write cache (BBWC) on the disk subsystem and how's it configured?
 On systems where disk has proved to be the bottleneck, and there are many small pieces of
data being written, I've seen better than a factor of 10 improvement by adding write cache
in this way.
>   
I'll look into that to be sure, but I don't think the HD is limiting.

D



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