New comment by pullmoll on void-packages repository

https://github.com/void-linux/void-packages/issues/26508#issuecomment-730645253

Comment:
1) You probably cannot expect a single hit between chromium-86 and chromium-87 because headers changed and a change in a central header (think `version.h`) prevents a cache hit.
2) You need to make sure to re-bootstrap your environment, i.e. do `./xbps-src zap` and `./xbps-src binary-bootstrap` again to make the `etc/conf` (not `etc/config` AFAICT) change take effect.
3) Any change in the compiler binary invalidates the entire current cache, because a checksum of the compiler binary (`/usr/bin/clang++` in this case) is used to make sure that compilation results will indeed be identical. So the update of llvm10 to llvm11 already invalidated all your existing cache entries for `clang` / `clang++`. You can clean and zap the cache (`ccache -C` and `ccache -Z`) in such a case, except perhaps if you also have lots of `gcc` and `g++` cache entries.

I have a separate 1TB SSD for ccache and currently have 653 GiB of 768 GiB used with a cache hit rate of 8.06%. I'm building literally tens of thousands of packages for all architectures and can confirm that `ccache` indeed works as it is supposed to.