Poudriere speed is improved by ccache use, introduced in D3486.
This change exports metrics for ccache, so we can offer visibility
on the cache current use and efficiency.
From a performance point of view, ccache_cache_hit_rate gives the hit %.
From a monitoring point of view, ccache_cache_size and ccache_max_cache_size
are a nice pair of values to watch, so we know when to increase cache size.
To get metrics for the common cache used by local ports and poudriere:
$ export CCACHE_DIR=/var/cache/ccache $ ccache-metrics
Ref T2039