## ccache

ccache is a compiler cache. It acts as a caching pre-processor to C/C++ compilers, using the -E compiler switch and a hash to detect when a compilation can be satisfied from cache. This often results in a 5 to 10 times speedup in common compilations.

The idea came from Erik Thiele wrote the original compilercache program as a bourne shell script. ccache is a re-implementation of Erik's idea in C with more features and better performance.

## Latest release

The latest release is ccache 2.4.

- Added CCACHE_READONLY option
- Added CCACHE_TEMPDIR option
- fixed handling of hard-linked compilers on AIX
- added O_BINARY support, to try and support win32 compiles
- show cache directory in stats output
- fixed handling of HOME environment variable

See the manual page for details on the new options.

You can get this release from the download directory

NOTE! This release changes the hash input slightly, so you will probably find that you will not get any hits against your existing cache when you upgrade.

## Why bother?

Why bother with a compiler cache? If you ever run "make clean; make" then you can probably benefit from ccache. It is very common for developers to do a clean build of a project for a whole host of reasons, and this throws away all the information from your previous compiles.

By using ccache you can get exactly the same effect as "make clean; make" but much faster. It also helps a lot when doing RPM builds, as RPM can make doing incremental builds tricky.

I put the effort into writing ccache for 2 reasons. The first is the Samba build farm (http://build.samba.org/) which constantly does clean builds of Samba on about 30 machines after each CVS commit. On some of those machines the build took over an hour. By using ccache we get the same effect as clean builds but about 6 times faster.

The second reason is the autobuild system I used to run for Quantum. That system builds our whole Linux based OS from scratch after every CVS commit to catch compilation problems quickly. Using ccache those builds are much faster.

## Is it safe?

Yes. The most important aspect of a compiler cache is to always produce exactly the same output that the real compiler would produce. The includes providing exactly the same object files and exactly the same compiler warnings that would be produced if you use the real compiler. The only way you should be able to tell that you are using ccache is the speed.

I have coded ccache very carefully to try to provide these guarantees.

## Features

- keeps statistics on hits/misses
- automatic cache size management
- can cache compiles that generate warnings
- easy installation
- very low overhead
- uses hard links where possible to avoid copies

## Documentation

See the manual page

## Performance

Here are some results for compiling Samba on my Linux laptop. I have also included the results of using Erik's compilercache program (version 1.0.10) for comparison.

| ccache | compilercache
--- | --- | ---
normal | 13m 4s | 13m 4s
uncached | 13m 15s | 15m 41s
cached | 2m 45s | 4m 26s

## How to use it

You can use ccache in two ways. The first is just to prefix your compile commands with "ccache". For example, you could change the "CC=gcc" line in your Makefile to be "CC=ccache gcc".

Alternatively, you can create symbolic links from your compilers name to ccache. This allows you to use ccache without any changes to your build system.

## Download

You can download the latest release from the download directory.

For the bleeding edge, you can fetch ccache via CVS or rsync. To fetch via cvs use the following command:

      cvs -d :pserver:cvs@pserver.samba.org:/cvsroot co ccache

To fetch via rsync use this command:

      rsync -Pavz samba.org::ftp/unpacked/ccache .

## Related projects

Here are some related programs you may find interesting

- distcc - a distributed compilation system
- cachecc1 - a gcc specific cache
- gocache - a cross platform compiler cache

## Mailing list

A mailing list is available for discussion of ccache.

Andrew Tridgell
bugs@ccache.samba.org