- Explain how to use sccache as ccache replacement
sccache helps avoid repeated recompilation for the same C, C++, and Rust 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 /etc/portage/patches 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 www-client/firefox or mail-client/thunderbird, without fear of losing multiple hours of code compilation due to a failure.
emerge --ask dev-util/sccache
Create the cache directory:
mkdir -p /var/cache/sccache
chown root:portage /var/cache/sccache
chmod 2775 /var/cache/sccache
Allow write access to the cache directory when running under sandbox:
# Allow write access to sccache cache directory SANDBOX_WRITE="/var/cache/sccache/"
Enable sccache support in make.conf:
RUSTC_WRAPPER=/usr/bin/sccache SCCACHE_DIR=/var/cache/sccache SCCACHE_MAX_FRAME_LENGTH=104857600
From now on all builds utilizing Rust compiler will try to reuse object files from the /var/cache/sccache cache.
SCCACHE_MAX_FRAME_LENGTH is needed to allow packages like www-client/firefox to compile.
The setup above will only enable sccache usage for Rust.
sccache can be enabled for the current user and re-use the same cache directory:
export RUSTC_WRAPPER="/usr/bin/sccache" export SCCACHE_DIR="/var/cache/sccache" export SCCACHE_MAX_FRAME_LENGTH="104857600"
Useful variables and commands
- Variable SCCACHE_DIR points to cache root directory.
- Command sccache -s shows cache hit statistics:
SCCACHE_DIR=/var/cache/sccache sccache -s
Compile requests 0 Compile requests executed 0 Cache hits 0 Cache misses 0 Cache timeouts 0 Cache read errors 0 Forced recaches 0 Cache write errors 0 Compilation failures 0 Cache errors 0 Non-cacheable compilations 0 Non-cacheable calls 0 Non-compilation calls 0 Unsupported compiler calls 0 Average cache write 0.000 s Average cache read miss 0.000 s Average cache read hit 0.000 s Failed distributed compilations 0 Cache location Local disk: "/var/cache/sccache/" Cache size 5 GiB Max cache size 10 GiB
Not like ccache, sccache can only read statistics from running instance. Those interested in statistics must manually spawn sccache server first.
- Handbook:AMD64/Working/Features#Caching_compilation_objects — how to use Ccache
- Ccache — helps avoid repeated recompilation for the same C and C++ object files by fetching result from a cache directory.