[ccache] Implementing a Read-only HTTP CCACHE_DIR(resurrect)

Anders Björklund anders at itension.se
Tue Dec 1 20:08:11 UTC 2015

vkr wrote:
> Hello,
> I stumbled across this thread -
> https://lists.samba.org/archive/ccache/2012q2/000879.html which is years
> old,
> Coincidentally, I did some work along similar lines already, without
> realizing there was this discussion about this topic here,
> and I appreciate some comments/suggestions on my approach so far.

This is interesting, there was some renewed interest in the memcached
patch that was proposed in the same timeabout frame (i.e. in 2013)


> Having cache on NFS is comparatively the easy option from configuration
> point of view, however, there can be environments where
> for whatever the reasons, NFS server is a few hops away, while there are
> other machines that are closer to the build farm, in which case,
> having a HTTP CCACHE_DIR does seemed like a reasonably better option as it
> involves less configuration havoc on every machine in the build farm.

It also has lots of problems with for instance locking (workaround
is included) and overhead when updating modification timestamps etc.

> Keeping the above as use case, I've implemented HTTP CCACHE_DIR in my fork
> - https://github.com/venkrao/ccache
> This is a very crude throw-away test from a beginner C Programmer, that
> does the following. Care has been taken to ensure it does behave like
> existing ccache to the extent I know so far, and I did have successful runs
> of modified ccache with no core/crash or surprise failures.

I haven't been able to test your code, but it does sound like there
are some shortcomings in the design (e.g. like it being read-only).

The repository has some issues, in that it has been disconnected ?
It also has a bunch of generated files, being imported from tarball.

> Unfortunately, in our existing environment I could not see visible
> improvement between our NFS based cache setup and this new approach.
> I cannot attribute the lack of performance to anything right now.

It could be inherent with HTTP, just like it was in NFS before ?
Using a local filesystem cache or a shared memcached seems better...

I gave up on _my_ http version, when I found the memcached version.
Will post some more details about my own version of it separately.


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