Kache: Zero-copy, compiler cache for Rust

Kache is a compiler cache for Rust, C/C++, and CUDA. It keys every compiler invocation by the content of its inputs, so a crate built once is restored instead of rebuilt in your next worktree, branch, or CI run. Outputs live in a local content-addressed store and can be shared through S3-compatible or filesystem remotes. Linux, macOS, and Windows are supported and release-tested.

Built by Kunobi.

Benchmarks · Kache vs sccache · CI setup

See how Kache shares build outputs across worktrees →

cargo install kache
kache init

Your Cargo commands do not change.

kache init sets rustc-wrapper in Cargo's config. On Unix it also adds the [env] keys for build-script C and C++. Run kache init --check to preview the changes, or kache init --no-service to skip the OS service.

cargo install needs Rust 1.95 or newer. Prebuilt packages exist for Homebrew, APT, AUR, winget, Scoop, Chocolatey, mise, and Nix. Release builds cover x86_64 and ARM on Linux, macOS, and Windows. See Install Kache for each channel.

After kache init, build the same revision in two temporary worktrees. Each gets its own target directory, so your existing build outputs stay in place. The second tree's report lists the hits and a bypass reason for every unit that still compiled.

Kache has three parts: a compiler wrapper, a local store, and an optional daemon.

• The wrapper parses each rustc ,rustdoc ,cc ,c++ , ornvcc invocation, hashes the inputs that change the output, and normalizes the machine-local paths that do not. Two worktrees of the same revision produce the same key.
• Wrappers that reach the same key at the same time join one flight, so the compiler runs once per key on a machine, however many Cargo processes ask for it.
• The store keeps outputs as content-addressed blobs. Identical bytes are stored once. Restores use copy-on-write clones where the filesystem supports them, so a second worktree costs little disk.
• The daemon serves remote lookups after a local miss and uploads new entries in the background.

Hits, misses, and passthroughs are reported per unit, and kache why-miss explains what changed. Read the architecture →

In a Firefox 151 benchmark with Kache 0.7.0 on macOS/APFS, the second worktree added about 3 GB of new data. Read the measurements and methodology →

For a comparison with sccache, read Kache or sccache?.

The scheduled benchmark workflow runs real cold and warm builds of Firefox, LLVM, SurrealDB, Lance, OpenDAL, cuda-oxide, and eza on Linux. Separate workflows build Firefox on Windows every night and compare Firefox with sccache once a week. It also measures how much of a Firefox build survives a source update.

Each run checks its own measurement validity and uploads reports, traces, and logs for 30 days. Treat timing or hit-rate numbers as evidence only when the individual job succeeds and its benchmark verdict is ok.

See the benchmark setup and report guide →

The official action installs Kache and wires it into the build:

- uses: kunobi-ninja/kache-action@v1

- run: cargo build --locked

See the CI guide for GitHub Actions and shell-based CI examples.

On Unix, kache init creates compiler-name shims and offers to add their directory to PATH in your zsh, bash, or fish startup file. Make, CMake, autotools, and Arch PKGBUILDs that call gcc by name then go through Kache, with no CC= edit or shell wrapper.

For managed dotfiles or another shell, set it up by hand:

kache install-shims
export PATH="$HOME/.local/lib/kache/shims:$PATH"

APT and AUR packages install /usr/lib/kache. Nix packages include the same symlinks in ${kache}/shims and ${kache}/lib/kache; see the Nix configuration example.

For makepkg, put the same assignment in ~/.makepkg.conf. Wrap extra names already on PATH with kache install-shims --from-path.

Kache inspects the real compiler invocation. Unsupported or unsafe invocations pass through. See C and C++.

The default local cache is:

• Linux: $XDG_CACHE_HOME/kache or~/.cache/kache
• macOS: ~/Library/Caches/kache
• Windows: %LOCALAPPDATA%\kache

Open the configuration editor with kache config, or edit the TOML file directly. A minimal S3-compatible remote looks like this:

[cache.remote]
type = "s3"
bucket = "my-build-cache"
region = "us-east-1"

Credentials come from the standard AWS environment variables or credential chain. See S3 setup and filesystem setup.

kache monitor                 # live build and cache activity
kache stats                   # hit rate, time saved, cache size
kache stats --last-build      # hits, misses, and bypass reasons of the latest build
kache stats --full --redact   # full report without cache keys and paths, for sharing
kache diff                    # compare the two newest sessions of one root
kache doctor                  # setup and integrity checks
kache install-shims           # Unix compiler-name PATH farm
kache why-miss <crate>        # explain the latest miss
kache list                    # inspect cached entries
kache gc                      # enforce cache limits
kache targets                 # target dirs, what each frees, deleted worktrees
kache clean --orphans --yes   # remove the targets of deleted worktrees
kache sync                    # pull from and push to the configured remote
kache daemon status           # inspect the background service

Run kache help <command> for exact flags. The command reference covers every top-level command.

To pass one build through without changing the setup, run it with KACHE_DISABLED=1.

For Kubernetes and GitOps, Kunobi Desktop lets you inspect clusters and manage Flux and Argo CD.

• Open a bug report when Kache behaves differently from the documentation.
• Request a feature for a missing compiler, remote backend, or build workflow.

git clone https://github.com/kunobi-ninja/kache.git
cd kache
cargo test --workspace --all-features

See CONTRIBUTING.md before opening a pull request.

Kache is licensed under the Apache License 2.0.