[ccache] Using ccache with memcached

[Wilson Snyder]

>On 25 November 2010 00:52, Henrik Goldman <hg at x-formation.com> wrote:
>> Hello,
>>
>> I wonder if anyone ever considered using memcached as an optional backend
>> for ccached?
>>
>> Here is the issue we're considering. In our C++ project we have a number of
>> developers doing their own local compilations. When any updates occurs (e.g.
>> they update to the latest source code from scm) the compilations are the
>> same for all the machines. Sure ccache is great when you re-do the
>> compilation, but here the compilation being re-done on a number of machines.
>> Using memcached would allow us to have a truly distributed cache that would
>> both help developers and machines in the build farm to speed up work.
>>
>> What do you guys think?
>
>I think it would be a pretty interesting idea.
>
>Obviously you would need to trust all the other clients writing into
>the cache, but that's probably feasible in this environment.
>
>A shared cache kept entirely in ram might grow fairly big, but it's
>not so expensive to get an 8GB or 16GB machine devoted to this.

Why don't you just put the cache on a NFS (/CIFS) mounted
volume?  With the most recent version this should work well.

If you already are, are you really doing enough writes to
swamp a NFS cache server?  It probably requires hundreds of
compiling clients; since we have over a hundred here and
don't see a bottleneck - with a single well performing NFS
server.

If you need more performance you can get a better NFS server
appliance (up to thousands of disks if you have the $$), or
on the cheap by striding the cache across 16 (or 256) small
NFS servers.

You can also serve NFS from a ram disk via loopback,
although if you give a machine enough memory, it's going to
keep a normal file system in RAM anyways, so using a ramdisk
primarily provides you with write bandwidth, not read
bandwidth nor latency.

Memcached would provide a nice benefit of providing
tolerance for machines going down, and somewhat better
latency, but perhaps the above ideas with the existing
version can deliver enough performance for you.

-Wilson