Caching

Caching build artifacts is a large quality of life improvement: typically, dependencies do not change too much, and not all of the crates in your project change all the time either. With a good build cache, compiling the project after small changes can become very fast.

Rust already has a local build cache in the target folder, but this is only useful for local development. In CI, the project is usually built from a clean checkout every time. A shared cache allows your team and CI to reuse compilation results across builds and machines.

sccache

sccache is a compiler caching tool developed by Mozilla (originally for Firefox builds). It wraps the compiler and stores the output of compilation in a shared cache. When the same source file is compiled again with the same flags, sccache returns the cached result instead of recompiling.

It supports multiple storage backends:

• Local disk
• Cloud storage (S3, GCS, Azure Blob Storage)
• Redis
• Memcached

You install it and tell Cargo to use it as a wrapper around rustc:

cargo install sccache
export RUSTC_WRAPPER=sccache
cargo build

You can also set this permanently in your .cargo/config.toml:

[build]
rustc-wrapper = "sccache"

After a build, you can check the cache statistics with sccache --show-stats to see hit rates and how much time was saved.

name: Build
on: [push]

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: dtolnay/rust-toolchain@stable
      - uses: mozilla-actions/sccache-action@v0.0.7
      - run: cargo build --release
        env:
          RUSTC_WRAPPER: sccache
          SCCACHE_GHA_ENABLED: "true"

For local development, sccache is most useful when you frequently switch between branches or work on multiple projects that share dependencies. The local disk backend requires no setup beyond installing sccache and setting the wrapper.

Reading