The droppable tombstone ratio is shaping up to be an important metric for us. We should collect, persist, and configure dashboards for it.
A couple of problems with this:
a) The metric is not included in o.a.cassandra.metrics, so as things stand, we cannot get at it with cassandra-metrics-collector, and b) each query is roughly equivalent to invoking sstablemetadata against each file, so reading it every collection interval would be too expensive (it doesn't change often enough to warrant that anyway). So for the time being, I will collect some ad hoc results using something like the following
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