zccache 1.0.20

A high-performance local compiler cache daemon

zccache

A blazing fast cpp compiler cache

Inspired by sccache, but optimized for local-first use with aggressive file metadata caching and filesystem watching.

Performance

Benchmark: 50 C++ files, warm cache

Scenario	Bare Clang	sccache	zccache	vs sccache	vs bare clang
Single-file, Cold	10.336s	17.292s	11.489s	1.5x faster	0.9x
Single-file, Warm	10.141s	1.331s	0.031s	43x faster	324x faster
Multi-file, Cold	9.898s	9.906s	10.337s	1.0x faster	1.0x
Multi-file, Warm	10.422s	9.809s	0.023s	419x faster	446x faster

Cold = first compile (empty cache). Warm = median of 5 subsequent runs. Single-file = 50 sequential clang++ -c unit.cpp invocations. Multi-file = one clang++ -c *.cpp invocation. sccache cannot cache multi-file compilations — its "warm" multi-file time is a full recompile.

Run the benchmark yourself: uv run perf

Build system integration (ninja, meson, cmake, make)

zccache is a drop-in compiler wrapper. Point your build system's compiler at zccache <real-compiler> and it handles the rest:

# meson native file
[binaries]
c = ['zccache', '/usr/bin/clang']
cpp = ['zccache', '/usr/bin/clang++']

# CMake
set(CMAKE_C_COMPILER_LAUNCHER zccache)
set(CMAKE_CXX_COMPILER_LAUNCHER zccache)

The first build (cold cache) runs at near-bare speed. Subsequent rebuilds (ninja -t clean && ninja, or touching source files) serve cached artifacts via hardlinks in under a second.

Single-roundtrip IPC: In drop-in mode, zccache sends a single CompileEphemeral message that combines session creation, compilation, and session teardown — eliminating 2 of 3 IPC roundtrips per invocation.

Session stats: Track hit rates per-build with --stats:

eval $(zccache session-start --stats --log build.log)
export ZCCACHE_SESSION_ID=...
# ... build runs ...
zccache session-stats $ZCCACHE_SESSION_ID   # query mid-build
zccache session-end $ZCCACHE_SESSION_ID     # final stats

Persistent cache: Artifacts are stored in ~/.cache/zccache/artifacts/ (or %LOCALAPPDATA%\zccache\artifacts\ on Windows) and survive daemon restarts. No need to re-warm the cache after a reboot.

Multi-file compilation (fast path)

When a build system passes multiple source files to a single compiler invocation (e.g. gcc -c a.cpp b.cpp c.cpp -o ...), zccache treats this as a fast path:

1. Each source file is checked against the cache in parallel.
2. Cache hits are served immediately — their .o files are written from the cache.
3. Remaining cache misses are batched into a single compiler process, preserving the compiler's own process-reuse and memory-sharing benefits.
4. The outputs of the batched compilation are cached individually for future hits.

This hybrid approach means the first build populates the cache per-file, and subsequent builds serve as many files as possible from cache while still letting the compiler handle misses efficiently in bulk.

Recommendation: Configure your build system to pass multiple source files per compiler invocation whenever possible. This gives zccache the best opportunity to parallelize cache lookups and minimize compiler launches.

Concurrency

The daemon uses lock-free concurrent data structures (DashMap) for artifact and metadata lookups, so parallel compilation requests from multiple build workers never serialize on a global lock.

Status

Early development — architecture and scaffolding phase.

Goals

• Extremely fast on local machines (daemon keeps caches warm)
• Portable across Linux, macOS, and Windows
• Correct under heavy parallel compilation (no stale cache hits)
• Simple deployment (single binary)

Architecture

See docs/ARCHITECTURE.md for the full system design.

Key components

Crate	Purpose
zccache-cli	Command-line interface (zccache binary)
zccache-daemon	Daemon process (IPC server, orchestration)
zccache-core	Shared types, errors, config, path utilities
zccache-protocol	IPC message types and serialization
zccache-ipc	Transport layer (Unix sockets / named pipes)
zccache-hash	blake3 hashing and cache key computation
zccache-fscache	In-memory file metadata cache
zccache-artifact	Disk-backed artifact store with redb index
zccache-watcher	File watcher abstraction (notify backend)
zccache-compiler	Compiler detection and argument parsing
zccache-test-support	Test utilities and fixtures

Building

cargo build --workspace

Testing

cargo test --workspace

Documentation

• Architecture
• Design Decisions
• Roadmap

License

Licensed under either of Apache License, Version 2.0 or MIT license at your option.