The ccache software maintains a cache to store compilation artefacts, so the next time you compile the same source file, you can get the compiled code from the cache. That speeds up a lot recompilation.
At Nasqueron, ccache is useful to speed up Poudriere builds to test FreeBSD ports. To be able to follow if the cache is useful, we devised a Grafana dashboard to expose metrics from ccache.
If you run ccache -s, it prints statistics. For example with ccache 3:
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$ ccache -V | head -n1 ccache version 3.7.12 $ ccache -s cache directory /var/cache/ccache primary config /var/cache/ccache/ccache.conf secondary config (readonly) /usr/local/etc/ccache.conf stats updated Sun Oct 6 13:56:59 2024 cache hit (direct) 571 cache hit (preprocessed) 309 cache miss 10089 cache hit rate 8.02 % called for link 1577 called for preprocessing 265 multiple source files 3 compiler produced no output 3 compiler produced empty output 4 compile failed 612 preprocessor error 292 bad compiler arguments 68 unsupported source language 14 autoconf compile/link 2829 no input file 426 cleanups performed 0 files in cache 24590 cache size 167.9 kB max cache size 5.0 GB |
Converted into OpenMetrics format, that gives:
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$ ccache-metrics # TYPE ccache_cache_directory info ccache_cache_directory_info{path="/var/cache/ccache"} 1 # TYPE ccache_primary_config info ccache_primary_config_info{path="/var/cache/ccache/ccache.conf"} 1 # TYPE ccache_secondary_config info ccache_secondary_config_info{path="/usr/local/etc/ccache.conf"} 1 # TYPE ccache_stats_updated counter ccache_stats_updated_total 1728223019 # TYPE ccache_cache_hit_direct counter ccache_cache_hit_direct_total 571 # TYPE ccache_cache_hit_preprocessed counter ccache_cache_hit_preprocessed_total 309 # TYPE ccache_cache_miss counter ccache_cache_miss_total 10089 # TYPE ccache_cache_hit_rate gauge ccache_cache_hit_rate 0.0802 # TYPE ccache_called_for_link counter ccache_called_for_link_total 1577 # TYPE ccache_called_for_preprocessing counter ccache_called_for_preprocessing_total 265 # TYPE ccache_multiple_source_files counter ccache_multiple_source_files_total 3 # TYPE ccache_compiler_produced_no_output counter ccache_compiler_produced_no_output_total 3 # TYPE ccache_compiler_produced_empty_output counter ccache_compiler_produced_empty_output_total 4 # TYPE ccache_compile_failed counter ccache_compile_failed_total 612 # TYPE ccache_preprocessor_error counter ccache_preprocessor_error_total 292 # TYPE ccache_bad_compiler_arguments counter ccache_bad_compiler_arguments_total 68 # TYPE ccache_unsupported_source_language counter ccache_unsupported_source_language_total 14 # TYPE ccache_autoconf_compile_link counter ccache_autoconf_compile_link_total 2829 # TYPE ccache_no_input_file counter ccache_no_input_file_total 426 # TYPE ccache_cleanups_performed counter ccache_cleanups_performed_total 0 # TYPE ccache_files_in_cache gauge ccache_files_in_cache 24590 # TYPE ccache_cache_size gauge ccache_cache_size 171929.6 # TYPE ccache_max_cache_size gauge ccache_max_cache_size 5368709120.0 # EOF |
Those metrics can then be published to a timeseries database like Prometheus.
The Python code to perform this conversion is available in our operations repository. It doesn’t have any dependency.
Important note about ccache versions. As we target FreeBSD and Poudriere, the code handles ccache 3. The parsing code need to be updated for ccache 4, as their statistics output format changed. Run ccache -svv to get the same kind of output under ccache 4, but we need to ignore section headers.