Migrating data and cleaning up my old desktop display head machine, I decided to check out my ccache statistics. This is a very old cache, having first started 2006-01-13. The oldest item in the present cache is 2008-01-12, but the statistics are valid for the entire period. hits 229k and 834k misses = approximately 21% hit rate. This wasn't any crazy repeated compiling of my own code, just a dedicated ccache directory for Portage to use.
cache hit 228637 cache miss 834113 called for link 100293 multiple source files 526 compile failed 20645 ccache internal error 14 preprocessor error 12425 cache file missing 9 bad compiler arguments 1 not a C/C++ file 39097 autoconf compile/link 183802 unsupported compiler option 34481 no input file 96690 files in cache 204344 cache size 1.8 Gbytes max cache size 2.0 Gbytes