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How to use ccache in GitHub Actions

C and C++ builds recompile everything on every run.

5 min read

C and C++ builds recompile everything on every run.

Why it happens

ccache's store is not persisted, so it cannot short-circuit identical compilations.

How to fix it

  1. Cache ~/.ccache keyed on the compiler version and source hash
  2. Set CMAKE_C_COMPILER_LAUNCHER and CMAKE_CXX_COMPILER_LAUNCHER to ccache
  3. Print ccache -s at the end of the job so hit rate is visible
  4. Set max_size high enough — the default is often too small for CI

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