The existing reservoir-sampling based latency metrics in HBase are not well-suited for providing accurate estimates of high-percentile (e.g. 90th, 95th, or 99th) latency. This is a well-studied problem in the literature (see  and ), the question is determining which methods best suit our needs and then implementing it.
Ideally, we should be able to estimate these high percentiles with minimal memory and CPU usage as well as minimal error (e.g. 1% error on 90th, or .1% on 99th). It's also desirable to provide this over different time-based sliding windows, e.g. last 1 min, 5 mins, 15 mins, and 1 hour.
I'll note that this would also be useful in HDFS, or really anywhere latency metrics are kept.