needed help in interpreting results

[Piotr Kadziolka]

The test was taken on low-end machine. Compared with nowdays hdd I had 
very, very small disk, so test couldn't be long. It took nearly 500 
minutes. It's to short time to let cron jobs to affect results. Besides 
there wasn't defined any jobs in cron and Squid logging was disabled. If 
it was related to Squid filling up what caused that peaks? I don't know 
details on how COSS works but at first moment I thought that it could be 
caused by writting data from stripe in memory into disk. But default size 
of stripe is 1 MB, so peaks would take place more, more frequently. I 
still have no idea what was the casue of peaks in trace. Where I can find 
documentation about COSS module?




Duane Wessels <wessels at measurement-factory.com> 
2008-08-27 01:22

To
Piotr Kadziolka <PKadziolka at acppharma.pl>
cc
users at web-polygraph.org
Subject
Re: needed help in interpreting results









On Tue, 26 Aug 2008, Piotr Kadziolka wrote:

> Hi,
>
> Some time ago I've made series of tests on Squid-2.5STABLE5. I wanted
> confirm and verify results obtained by Duane Wessels in his book about
> Squid. Duane measured how Squid performace can depends on filesystem
> performance. I took all tests on the same machine in  identical
> environment but I obtained strange results for COSS (coss.png).
>
>
> Could someone interpret this results? Is anyone who can give me
> explaination about this periodical peak in response time? Adjustment
> algorithm in the workload (attached file pm4-pf2.pg) take care about
> misses and hits and take action when value exceeds or fell below,
> respectively, 3.0 and 0.25 sec. At second image (diskd.png) which 
contains
> trace for diskd there is no similar peak.

Whats the time span of the test?  Any chance that they could be
caused by some daily cron job?  But then you'd kind of expect to
see the effect in the diskd data too.  Also the way that the peaks
take longer to decay make me think that its related to Squid filling
up rather than a system cron job.

Duane W.

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