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Re: Trials with memcached

From: Tony Butt <Tony.Butt_at_cea.com.au>
Date: Fri, 8 Jul 2011 13:45:23 +1000

On Thu, 2011-07-07 at 17:31 -0700, Geoff Hoffman wrote:

        Tony -

        Strange results to be sure. You probably thought of all this, but...

        Did you check Memcached is working correctly without Subversion?

It seems to be - reviewboard works OK, and running memcached-tool shows cache hits, etc, as expected.

        Did you check the results of checking out or updating the 2nd or 3rd time?

I ran the update several times, it was consistent.
I did not do the original checkout more than once.

        In other words, it may take longer the first time because every object in the repo has to be checked for existence/expiry in the cache.

Yes - memcached-util showed plenty of cache hits after the initial checkout.

        Did you check that you gave Memcached enough memory to fit the entire 250mb repo (comfortably) in RAM?

Configured memcached with 256M memory. Might not be enough. I will try with 512M, and watch the performance on the server.
Our entire repository is several gigabytes in size, checkout sizes might be around 500M or so. If populating the cache causes a 6x slowdown, it is probably not worth it for 20 developers anyway.
The issue there is that it blows out our 'worst case' timing.

        If not then memcached itself tries to use swap space?

        32-bit or 64-bit VM?

PAE kernel,

        Did you try it on physical hardware?

No - we have a test machine that runs on physical hardware, I will try it there when I have time.

        On Thu, Jul 7, 2011 at 4:59 PM, Daniel Shahaf <d.s_at_daniel.shahaf.name> wrote:

                This doesn't address memcached directly, but there has been a /lot/ of
                work on server-side optimization and caching in 1.7 (also for
                non-memcached-backed caches).
                You might want to take 1.7.0-alpha3 for a spin...
                Tony Butt wrote on Wed, Jul 06, 2011 at 15:20:27 +1000:
> We are running subversion 1.6.17 on a vmware hosted server. We recently
> reconfigured the server to give 4 virtual CPUs (up from 1), and a
> significant amount of memory.
> In order to spruce up our performance a little, I looked into the use of
> memcached with subversion again, found the correct config parameter, and
> set it up. Our server is running Ubuntu 10.04, Apache 2.2. Access
> mechanism is http (of course). The client used is running Ubuntu 11.04,
> and svn commandline (1.6.17 also)
> The results were interesting, to say the least.
> Checkout of a tree, about 250M in size:
> Without memcached, 1 1/2 to 2 minutes, varies with server load
> With memcached, 12 minutes (!)
> Update of the same tree,
> Without memcached, 9 seconds
> With memcached, 14 seconds - repeated several times, similar results.
> I am not sure what anyone else's experience is, but we will not be
> enabling memcached for subversion any time soon.
> --
> Tony Butt <tjb_at_cea.com.au>
> CEA Technologies

Tony Butt <tjb_at_cea.com.au>
CEA Technologies
Received on 2011-07-08 06:15:19 CEST

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