Ccache

Article description::helps avoid repeated recompilation for the same C and C++ object files by fetching result from a cache directory.

Compiler cache is typically useful for:


 * Developers who rebuild the same/similar codebase multiple times and use to test patches.
 * Users who frequently play with USE-flag changes and end up rebuilding the same packages multiple times.
 * Users who use live ebuilds extensively.
 * Installing very big ebuilds, such as Chromium or LibreOffice, without fear of losing multiple hours of code compilation due to a failure.

Initial setup
Simply enable support in :

Done! From now on, all builds will try to reuse object files from the cache at.

Enabling ccache for certain packages
See.

ccache.conf
Example config:

Compression
ccache has the ability to perform compression on content. To enable it and set the compression level, edit ccache.conf:

Man page
Manual page for (see ) is a great source of various knobs to make caching more robust and aggressive.

General notes
works by prepending to PATH variable:

triggers the same behavior in Portage.

You can also enable for your current user and reuse the same cache directory:

Useful variables and commands
Some variables:


 * Variable CCACHE_DIR points to cache root directory.
 * Variable CCACHE_RECACHE allows evicting old cache entries with new entries:

See for many more variables.

Some commands:


 * Command shows cache hit statistics:


 * Command drops all caches:

See for many more commands.

is a wrapper
To pass through a binary, the following entry is suggested for :

Also,  has a nice side-effect of not invalidating your cache if compiler itself was rebuilt without version changes.

Caveats
Before using advanced options, make sure you understand what is being used as a cache key by. By default these are:


 * Timestamp and size of a compiler binary (beware of shell and binary wrappers)
 * Compiler options used
 * Contents of a source file
 * Contents of all include files used for compilation