There were multiple questions about compaction / related config values.
In general, I would say: you don’t need to touch them. Defaults should work most of the time.
But if you are interested about the beauty of internals, and manual tuning, I created a video to explain them.
(Or at least an attempt to explain them 
)
Fortunately it’s already quite long, even if I didn’t touch a few topics…
--hashstore.compaction.alive-fraction float
--hashstore.compaction.probability-power float
--hashstore.compaction.rewrite-multiple float