Don't rebuild textfile metricsfamily help text for the same name every time #3175
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Signed-off-by: Mark Knapp <[email protected]>
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This "optimization" shouldn't really be necessary in 99.99..% cases, but we recently ran into a memory usage issue because we had a huge number of processes dumping a few of the same metrics into their own textfile collector paths. Because this builds a help text for metricsfamily that is comprised of the names of all files with that same metric, this blew up the memory usage of building and storing all those help texts. So this change caches the help text for a given mf.Name, and doesn't recompute/store it every time.
To test the memory usage change, I dumped 5000 textfiles into a directory, and checked the process memory usage with and without this change. Before the change, node exporter reported
process_resident_memory_bytes 3.608977408e+09, or >3G of memory. After this it was onlyprocess_resident_memory_bytes 3.0969856e+07, or ~30M.