sccache - Shared Compilation Cache

Sccache is a ccache-like tool. It is used as a compiler wrapper and avoids compilation when possible, storing a cache in a remote storage using the S3 API.

It works as a client-server. The client spawns a server if one is not running already, and sends the wrapped command line as a request to the server, which then does the work and returns stdout/stderr for the job. The client-server model allows the server to be more efficient in its handling of the remote storage.

Sccache can also be used with local storage instead of remote.

Requirements

sccache is a Rust program. Building it requires cargo (and thus rustc). sccache currently requires Rust 1.12.

We recommend you install Rust via Rustup. The generated binaries can be built so that they are very portable, see scripts/build-release.sh.

Build

$ cargo build [--release]

Installation

$ cargo install

Usage

Running sccache is like running ccache: wrap your compilation commands with it, like so:

$ sccache gcc -o foo.o -c foo.c

Sccache (tries to) support gcc, clang and MSVC. If you don't specify otherwise, sccache will use a local disk cache.

You can run sccache --start-server to start the background server process without performing any compilation.

You can run sccache --stop-server to terminate the server. It will terminate after 10 minutes of inactivity.

Running sccache --show-stats will print a summary of cache statistics.

Storage Options

sccache defaults to using local disk storage. You can set the SCCACHE_DIR environment variable to change the disk cache location. By default it will use a sensible location for the current platform: ~/.cache/sccache on Linux, %LOCALAPPDATA%\Mozilla\sccache on Windows, ~/Library/Caches/sccache on OS X.

If you want to use S3 storage for the sccache cache, you need to set the SCCACHE_BUCKET environment variable to the name of the S3 bucket to use.

The environment variables are only taken into account when the server starts, so only on the first run.

Debugging

You can set the SCCACHE_LOG_LEVEL environment variable to debug or trace (not recommended, it's very verbose) to cause sccache to output more fine grained logging about what it is doing. A log file named sccache.log will be output in the current working directory whenever sccache is invoked.

Alternately, you can run the server manually in foreground mode by running SCCACHE_START_SERVER=1 SCCACHE_NO_DAEMON=1 sccache, and send logging to stderr by setting the RUST_LOG environment variable, the format of which is described in more detail in the env_logger documentation.

You can set the SCCACHE_ERROR_LOG environment variable to a path to cause the server process to redirect its standard error output there, in order to capture the output of unhandled panics. (The server sets RUST_BACKTRACE=1 internally.)

Known caveats

(and possible future improvements)

• Sccache doesn't try to be smart about the command line arguments it uses when computing a key for a given compilation result (like skipping preprocessor-specific arguments)
• It doesn't support all kinds of compiler flags, and is certainly broken with a few of them. Really only the flags used during Firefox builds have been tested.
• It doesn't support ccache's direct mode.
• It doesn't support an option like CCACHE_BASEDIR.