memcached on systems with small RAM

[Hans Kramer]

Hi,

I am using memcached on a system with very modest RAM: 64Mb to be precise (an Artila Matrix 504).

I have specified -M 1 -t 1 to reduce the memory allocated by memcached. 

Now RSS is always modest and around an explainable value, however, VSZ is at least 20Mb and with every

thread I add VSZ increases with at least 6 Mbytes. If I understand this correctly, this relative "high" VSZ, increases the oom_score

a lot. Hence I would like to reduce unnecessary alloc as much as possible. 

I have briefly looked at the memcached source and I cannot any significant mallocs. Is this perhaps coming from the libevent

library?

Any insights will be helpful.

Kind regards

Hans

[dormando]

You'll run into a few problems... -m 1 won't work the way you think since
it'll force-allocate one slab page per slab class. we don't have a
fallback mode to cut that down.

We also don't do anything to detune the thread stack size (which is
probably 2mb still?), plus a handful of allocations around each worker
thread (the new event base, connection buffers, etc).

That still seems sort of high, but thread stacks + etc would account for
quite a bit of it. You can also try reducing the size of the hash table..
that could show up as VSZ if you haven't written anything into it yet.

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[Hans Kramer]

Thanks, I will look into that.

Hans

[Perrin Harkins]

You might want to look at alternatives in that kind of setup. For example, BerkeleyDB is quite a bit faster than memcached when your cache is just on one local system. The advantages of memcached come into play when you have a large cache across multiple machines.

- Perrin

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[Hans Kramer]

Doesn't BerkelyDB write to disk? (of course I could use a tmpfs...... hmmm )

And I us  the auto expire of items in memcache....

Thanks for the tip, I definitely will consider it!

Hans

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[Perrin Harkins]

It does write to disk, so maybe it's not appropriate for your use. It is widely used in embedded systems though.

[Hans Kramer]

Thanks Perrin,

it's definitely an alternative!

Hans