Cassandra: enforce chunks size on compressed data

[sylvlecl]

• Do you want to request a feature or report a bug?

Improvement.

• What is the current behavior?

Cassandra AFS implementation stores data by cutting it in chunk and gzipping each chunk.
Therefore, the chunk size does not determine the size of chunks which are actually stored.

• What is the expected behavior?

It would make more sense to enforce the chunk size on actually stored data, i.e on gzipped data.
It will allow to really decide the size of data chunks stored in Cassandra.

Also, the chunking logic should be separate from the compression logic, and from the underlying storage, to make it more testable. A possibility is to have a dedicated ChunkedOutputStream class, which would dump byte[] chunks of a given size to an arbitrary consumer (or, possibly, a delegate output stream ...).

• What is the motivation / use case for changing the behavior?

Improved mastery of data stored in database. Also, it would help separate more the compression and chunking steps, which will help implement #58 .