[ccache] Using ccache with memcached

[Henrik Goldman]

On 25-11-2010 13:08, Wilson Snyder wrote:

> We have about 100 machines, with about 400 cores - a mix of
> older 2 socket up to modern 12 core systems.  Compiles are
> ~~10% of the work load.  The NFS server with CCACHE_DIR has
> 6 RAID-5 disks; it does other things too, not just ccache.
> We decided to bond 4 ethernet ports into the NFS server as
> we saw occasional bottlenecks exceeding 1GbE out of that
> server.
>

Quite interesting. Why does the compilers only take 10% of the time? Are 
you saying that ccache does the rest 90%?

>
> Managing CIFS/NFS isn't a big deal mostly because most IT
> departments already know how to manage CIFS/NFS.  Also, I'd
> be a little surprised if your site doesn't have shared CIFS
> drives already.
>

Sure we have. Actually I took the time to try it out with ccache v2.4 
(since it's the only Windows version currently available, excluding the 
various patches that may or may not work on the latest version). To my 
surprise it was so slow that it simply didn't make any sense. In many 
cases ccache took longer time than the real compiler would have to do 
the compilation.

In our environment we're already using Xoreax Incredibuild to speed up 
the compilation. While Incredibuild is good and does speed up the build 
then it doesn't solve the problem of re-doing the same steps multiple 
times for each developer. This is why I believe ccache would enhance 
Incredibuild even further.

I should say that if we could be compiling on linux only then gcc is so 
fast compared with Visual C++ that even a single core machine can 
compare with a Incredibuild cluster of 3-4 machines. Unfortunately we're 
stuck with these tools though...

>> I see that memcached is limited to 1 mb data per key. Naturally this
>> causes some troubles as many files would either not be cached or you'd
>> need to split it up to more keys.
>
> Good point, forgot about that.
>

I'd say that this is a sacrifice possible to live with though. For 
majority of source files they are within the limits.

-- Henrik