Improvements to rowset compaction policy (KUDU-1400) design doc

[William Berkeley <wd...@gmail.com>]

Hi Kudu devs. I've written a detailed design doc proposing some changes to
compaction policy that should help improve the unfortunately common
situation where Kudu has bad scan performance because of many small rowsets
that are not compacted together.

Here it is:
https://docs.google.com/document/d/1yTfxt0_2p5EfIjCnjJCt3o-nB9xk-Kl2O8yKTA1LQrQ/edit?usp=sharing

It should be open for comments.

It requires understanding the existing compaction policy, and is fairly
technical, but I would appreciate any comments or suggestions that others
have. I included a review of the current compaction policy in the document.

Thanks!
-Will