In Carbon Metrics , the TImers and Histograms use the default reservoir
provided by the Dropwizard Metrics  library.
Currently there is no support to change this reservoir implementation in
Carbon Metrics. Therefore we are working on supporting a set of reservoirs
in Carbon Metrics.
The HdrHistogram  is a popular histogram implementation and it has lot
of useful features for us. For more info, see . One major advantage for
us is that HDR Histogram maintains a fixed cost in both space and time.
When using HdrHistogram as reservoir, we can also a solve a problem with
the default Exponentially Decaying Reservoir when publishing metrics events
to WSO2 Data Analytics Server. The problem is explained in . With HDR
Histogram, we can reset the snapshot when reporting to WSO2 DAS.
We are going to integrate HDR Histogram into the next Carbon Metrics
release, which is based on Carbon 5.x
We don't have plans to do any release of Carbon Metrics based on Carbon
4.x. If anyone needs the HDR Histogram as a reservoir, we'll be able to do
changes in 1.x.x  branch and do a release.
Associate Technical Lead | WSO2, Inc. | http://wso2.com/
Lean . Enterprise . Middleware
Contact: +IsuruPereraWSO2 <https://www.google.com/+IsuruPereraWSO2/about>
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