1. MonoTime/MonoDelta
MonoTime: The MonoTime represents a particular point in time, relative to some fixed but unspecified reference point.
MonoDelta: The MonoDelta class represents an elapsed duration of time, the delta between two MonoTime instances.
2. CountDownLatch
This is a C++ implementation of the Java CountDownLatch
NOTE: This patch would modify all Backend's data.
And this will cause a very long time to restart be.
So if you want to interferer your product environment,
you should upgrade backend one by one.
1. Refactoring be is to clarify the structure the codes.
2. Use unique id to indicate a rowset.
Nameing rowset with tablet_id and version will lead to
many conflicts among compaction, clone, restore.
3. Extract an rowset interface to encapsulate rowsets
with different format.
