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 Amazon Simple Cloud Storage Service (S3) API, the Google Cloud Storage (GCS) API, or Redis.
Sccache now includes experimental Rust support.
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.
Table of Contents (ToC)
Sccache is a Rust program. Building it requires
cargo (and thus
rustc). sccache currently requires Rust 1.19.
We recommend you install Rust via Rustup. The generated binaries can be built so that they are very portable, see scripts/build-release.sh. By default
sccache supports a local disk cache. To build
sccache with support for
Redis cache backends, add
--features=all or select a specific feature by passing
redis. Refer the Cargo Documentation for details.
$ cargo build [--features=all|redis|s3|gcs] [--release]
$ cargo install
Running sccache is like running ccache: wrap your compilation commands with it, like so:
$ sccache gcc -o foo.o -c foo.c
or use it with rust, like so:
$ RUSTC_WRAPPER=[path to sccache] cargo build
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.
sccache --show-stats will print a summary of cache statistics.
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, and
~/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. You can use
AWS_SECRET_ACCESS_KEY to set the S3 credentials and if you need to override the default endpoint you can set
SCCACHE_ENDPOINT. To connect to a minio storage for example you can set
SCCACHE_REDIS to a Redis url in format
redis://[:<passwd>@]<hostname>[:port][/<db>] to store the cache in a Redis instance.
To use Google Cloud Storage, you need to set the
SCCACHE_GCS_BUCKET environment variable to the name of the GCS bucket.
If you're using authentication, set
SCCACHE_GCS_KEY_PATH to the location of your JSON service account credentials.
By default, SCCACHE on GCS will be read-only. To change this, set
SCCACHE_GCS_RW_MODE to either
Important: The environment variables are only taken into account when the server starts, so only on the first run.
You can set the
SCCACHE_LOG_LEVEL environment variable to
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
(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