As part of
YARN-5109 we introduced several KeyConverter classes.
To stay consistent with the existing LongConverter in the sample patch I created I made these other converter classes singleton as well.
In conversation with Sangjin Lee who has a general dislike of singletons, we discussed it is best to get rid of these singletons and make them simply instance variables.
There are other classes where the keys have static methods referring to a singleton converter.
Moreover, it turns out that due to code evolution we end up creating the same keys several times.
So general approach is to not re-instantiate rowkeys, converters when not needed.
I would like to create the byte rowKey in the RowKey classes their constructor, but that would leak an incomplete object to the converter.
There are a few method in TimelineStorageUtils that are used only once, or only by one class, as part of this refactor I'll move these to keep the "Utils" class as small as possible and keep them for truly generally used utils that don't really belong anywhere else.