Investigate adding ASYNC methods to Accumulo

[keith-turner]

In #593 async commit was added. The actual asynchronous writes to Accumulo were done in a hacky way that works, but is sub-optimal. The reason the current method is sub-optimal is that mutations and conditional mutations that are finished may not trigger follow on actions immediately until other unrelated data is processed. If the Accumulo itself supported async callbacks it could make the callbacks immediately when something finished processing.

[joshelser]

If the Accumulo itself supported async callbacks it could make the callbacks immediately when something finished processing.

Doesn't Thrift generate async service interfaces (and we just ignore it now)?

[keith-turner]

Doesn't Thrift generate async service interfaces (and we just ignore it now)?

Oh yeah I remember seeing that. I had not even thought that far ahead. I was just thinking of adding something to the existing client side code that informs you sooner when something is done. Once the callback mechanism is in the API it can gradually be pushed further and further in the implementation.