OakIncrementalIndex has a Plain mode

[sanastas]

Hi Everybody,

Please take a look on the following Oak Incremental Index Pool Request. Below please find a list of the help material. Although we will soon present also the performance results, we would like to hear your thoughts and comments from the correctness and software engineering point of views.

Thanks,
Anastasia

In continuation to our great talk yesterday (where we agreed about publishing a PR for Oak Incremental Index for Druid), hereby please find some reading material about Oak. The pool request itself will be ready for tomorrow. I would strongly suggest to read some of the documentation prior to looking on the code, as it may make the last task easier and clearer. As I said the Oak is now an open source library (https://github.com/yahoo/Oak) and its README might help you to understand the Oak's interface and new Druid's code.

Recall we had an issue#5698 about Oak Incremental Index (#5698) and there you can find another useful documents to start from. We will publish the latest single-thread ingestion benchmark results tomorrow, together with the pool request. Feel free to ask questions!

Files from the issue:

1. Oak Introduction: https://github.com/druid-io/druid/files/1946175/OakIntroduction.pdf
2. Oak Details Presentation: https://github.com/druid-io/druid/files/1946182/OAK.Off-Heap.Allocated.Keys.pptx
3. Suggested Refactoring: https://github.com/druid-io/druid/files/1947353/Incremental.Index.Refactoring.Suggestion.pdf
4. Some additional Oak results: https://github.com/druid-io/druid/files/1959106/OakMap.OnHeap.with.Integer.Values.pdf

[b-slim]

@sanastas thanks will try to take look by the end of this week.