Re: [squid-users] Squid Performance (with Polygraph)

What you may need to do is run the tests at lower req/sec's to find out where
its "stable"; or actually run Polmix-4 up properly.

Disk caches - UFS to a large extent, COSS somewhat - take a while to reach
a 'steady state'. With UFS (which I think you're using here, right?) you end
up initially laying down objects in some kind of linear fashion on disk, then
over time some objects are replaced and others aren't; you end up with
no temporal locality and various types of fragmentation.

Furthermore, if you're using datacomm-1 then you should know that the working
set increases without bounds over time - squid writes all of the cachable
objects to disk even though there's no chance of reading them back.

Try stopping the test and restarting squid but don't clear out the cachedir;
see if the performance takes that long to drop or whether it drops immediately.

I'd love to help out more but my only test environments right now have one
IDE disk in them; the most "disk plentiful" array I have is a Sun E250.
So its difficult to replicate results :>)

Adrian

On Wed, Nov 14, 2007, Dave Raven wrote:
> Hi Adrian and all,
> Sorry it's taken me so long to get back but I wanted to be sure I had all
> my ducks in a row. I couldn't find a program to graph what we needed, so I
> wrote a small script to log results - I've now done multiple tests, with
> multiple disk types etc and settled on using diskd as it lasts by far the
> longest. I'm graphing tps (transactions per second) on the drives and there
> is no plateau but a steady rise.
>
> Right now the best configuration I have (from my tests) is 2xLSI MegaRaid
> SCSI U320-1 controllers, with 4 Seagate Cheetah 15K.5 drives on each of
> them. In this configuration it lasts longer than the SATA controller, but
> exhibits the exact same behavior.
>
> With 800RPS my CPU usage never goes over 50%. When I start the cache my TPS
> across all the drives starts at about 400, and remains there for a few
> minutes - 10->20 probably. After that it begins a steep climb, which later
> flattens out a bit. This is the pattern seen in all of my tests (only the
> time and total tps differ).
>
> >From my reading it would appear that the original steep climb is because
> buffers become full - I wonder why it wouldn't write to the drives at full
> speed to start with if needed, but this part I understand I guess. The
> confusing part is why after that does it slowly and steadily rise - forever.
>
>
> For example, my 800RPS test runs for 240 minutes (graph of the TPS is
> attached to email), until it reaches the max tps the controller/drives seem
> to be able to handle, and fails. If I do it at 600RPS it lasts 350 minutes,
> also climbing though until it fails. At 1200 RPS it fails after 30 minutes.
>
> What is causing it to constantly climb - surely if it was a queue or build
> up of some type it's not reasonable to assume it might take > 300 minutes to
> actually break ? If that was the case it obviously has more steam in the
> first 100 minutes so why not utilize it?
>
> I have graphs available for all the tests, and I can arrange any
> stats/figures/configs etc needed - even access. I have run it at 1200 RPS
> for 18 hours with a null cache directory and it did not fail, so it's
> definitely disk drive handling (I guess) - but 350 minutes before it
> actually fails, and a slow, steady, predictable pattern? If it was
> plateau'ing like originally suggested I'd agree it's obviously hitting a
> limit - but my "rawio" tests show each drive is capable of 450 random
> writes/reads per second which is far higher than its doing.
>
> Thanks
> Dave
>
>
> -----Original Message-----
> From: Adrian Chadd [mailto:adrian@creative.net.au]
> Sent: Saturday, November 10, 2007 12:13 AM
> To: Dave Raven
> Cc: 'Adrian Chadd'; squid-users@squid-cache.org
> Subject: Re: [squid-users] Squid Performance (with Polygraph)
>
> On Fri, Nov 09, 2007, Dave Raven wrote:
> > Hi Adrian,
> >
> > It works for the full 4 hours with a null cache directory. How would
> > I see any kind of stats/information on disk IO? From the stats I can see
> so
> > far, the disk stats don't change at all when it fails ...
>
> That'd be because you're probably maxing the disk system out early on and
> what you're seeing is a slowly-growing disk service queue?
>
> > I'm currently using COSS, but I've also tried this with ufs and diskd
> (with
> > the same results, just different times that it fails after).
>
> COSS should handle small object loads better but some have reported little
> benefit beyond a pair of COSS disks.
>
> Try graphing the aggregate disk and per-disk transactions/second; I bet
> you'll find it plateau'ing relatively quickly early on.
>
>
>
>
> Adrian
>
> --
> - Xenion - http://www.xenion.com.au/ - VPS Hosting - Commercial Squid
> Support -
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