openstack team mailing list archive

[Jesse Andrews <anotherjesse@xxxxxxxxx>]

Agree that there are pros and cons to caching at different layers.

As for plugins, in most places where we support memcache we revert to
an in-memory cache if it isn't configured.

The work that was done during essex was to make the metadata service
use either an external cache or internal cache.  When an cloud-init
based image boots it makes dozens of calls to get data, which results
in dozens of RPC calls to nova-network to map IP to instance and then
to the DB to load data.

---------

Background info: The in-process cache I commited is actually the code
previously known as the "fake" memcache, moved from nova/tests to
nova/common.  The reason for the move is two-fold: 1) the code was
already in use as an in-memory cache in other locations in the code 2)
nova/tests isn't included in most (all?) packagings.

Also Josh Harlow has been researching better alternatives for
in-memory caches for python (rather than re-inventing the wheel -
which I started here: https://github.com/cloudbuilders/millicache ...)

----------

So ya, I think a summit proposal would be good.

Jesse

On Thu, Mar 22, 2012 at 8:06 AM, Sandy Walsh <sandy.walsh@xxxxxxxxxxxxx> wrote:
> o/
>
> Vek and myself are looking into caching strategies in and around Nova.
>
> There are essentially two approaches: in-process and external (proxy).
> The in-process schemes sit in with the python code while the external
> ones basically proxy the the HTTP requests.
>
> There are some obvious pro's and con's to each approach. The external is
> easier for operations to manage, but in-process allows us greater
> control over the caching (for things like caching db calls and not just
> HTTP calls). But, in-memory also means more code, more memory usage on
> the servers, monolithic services, limited to python based solutions,
> etc. In-process also gives us access to tools like Tach
> https://github.com/ohthree/tach for profiling performance.
>
> I see Jesse recently landed a branch that touches on the in-process
> approach:
> https://github.com/openstack/nova/commit/1bcf5f5431d3c9620596f5329d7654872235c7ee#nova/common/memorycache.py
>
> I don't know if people think putting caching code inside nova is a good
> or bad idea. If we do continue down this road, it would be nice to make
> it a little more modular/plug-in-based (YAPI .. yet another plug-in).
> Perhaps a hybrid solution is required?
>
> We're looking at tools like memcache, beaker, varnish, etc.
>
> Has anyone already started down this road already? Any insights to
> share? Opinions? (summit talk?)
>
> What are Glance, Swift, Keystone (lite?) doing?
>
> -S
>
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