A few observations:
- That’s a quite old version of metrics. Cassandra should upgrade.
- The snapshot API used between reservoirs and reporters is unfortunately very allocation heavy (that’s one of the things I’ve been thinking about how to address in metrics 4), but even so, 1GiB seems excessive, so something is probably not right.
- Is Cassandra configuring its exponential decay reservoirs with large sizes? The default (at least in metrics 3) is 1028, which is not crazy big. How many reservoirs (vs samples) exist in your heap dump?
- ExponentiallyDecayingReservoir (as it’s called in metrics 3 at least) is both incorrect for non-normal distributions, which includes most things you’d probably want to measure with metrics, and allocation-heavy even for a reservoir. In some world where Cassandra uses metrics 3, use
https://bitbucket.org/marshallpierce/hdrhistogram-metrics-reservoir instead, assuming you’re measuring things like latency. See that url for more on why.
-Marshall
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