[Hawkular-dev] [Metrics] Pluggable aggregation functions: next steps

Hi, I have looked at Aakarsh's repo: https://github.com/Akki5/hawkular_plugin/ It's a good start with an interface describing a doubles to double function, a classloader for implementation loading and a set of initial implementations. In order to integrate this work into Metrics, I think we should follow the following steps: ===== #1 Change the contract Doubles to double works great for avg/min/max/... functions on gauge metrics. But we need to consider other metric types. Also, the interface should not only accept data point values, but whole data points. Because some functions need the timestamp to compute the result. % of up availability is a good example. And functions may return different types: Double, Long, AvailabilityType. #2 Update configuration options to let the user set a plugins directory Metrics doc needs will have to be updated. #3 Create a function repository for each metric type We can build on JDK's service loader + Aakarsh's classloader implementation. #4 Add builtin aggregate functions Extract existing Metrics code (min, max, avg, % of up avail, downtime duration) into builtin functions. #5 Document the process of implementing a pluggable function We need to think about function naming as well. Should we use a prefix to identify a builtin function? ===== I will start another thread to discuss REST and Core API data query changes. Thoughts? Thanks, Thomas