Question concerning cpu utilization and memcached...

[Brad Fitzpatrick]

The python module on danga.com is old and unmaintained.  People using
memcached in production w/ python use some other module, tummy I
think:

    http://www.python.org/pypi/memcached/1.2_tummy3

Or are you using that one?

- Brad


On Thu, 28 Apr 2005, Christopher Gillett wrote:

> Environment:  FreebBSD 4.9, memcached-1.1.12, libevent 1.0c,
> python-memcached-1.2
> Issue:  Very heavy CPU utilization during get() processing
>
> I googled around and didn't find anything useful on this, so please be
> gentle if this question is a repeat of a previous discussion.  :-)
>
> I've spent the last couple days building out a memcached-based front end
> for one of our systems.  It caches a little over 1 million items, where
> the key is fairly short, and the content is also very short.  We query a
> good sized database and load everything in cache, and then run all
> lookups out of cache.  Performance has been excellent.  In testing in a
> grid configuration with 30+ nodes I am getting 500-600 cache hits per
> second on all nodes simultanesously which is really good (especially
> considering that we're using Python to drive the process).  I do observe
> one troubling behavior that I'm curious to know more about.
>
> I configured memcached to run on 9 servers at 250 mb/server.  When the
> cache is loaded, it looks like all instances are fairly evenly loaded
> (memory stats are virtually identical for all instances).  However, when
> we start running get()s I note that 1 of the 9 machines gets extremely
> busy in terms of CPU utilization, while the rest of the machines load
> fairly evenly.  For example, in one stress test I ran, the CPU
> utilization across 8 nodes averaged 5-6%.  One node, however, had
> utilization approaching 80%.  I am worried about having CPU utilization
> issues deploying this into production as we are running many CPU
> intensive processes on the same set of machines.  I also noticed this
> same behavior early on testing with just two instances of memcache
> running.
>
> Has this type of behavior been observed by others?  Any information as
> to what causes this or how to avoid it?
>
> Thanks for any insight....
> Chris Gillett
>
>