The 'transform' feature, where REST can be instructed, via a table attribute, to apply a transformation (e.g. base64 encoding or decoding) to a (sub)set of column values before serving them up to a client or storing them into HBase, was added some time ago at the request of Jack Levin. I have since come to regret it, it was not a well thought out feature:
- This is really an application concern.
- It adds significant overhead to request processing: Periodically a HBaseAdmin is used to retrieve the table descriptor, in order to scan through table attributes for transformation directives.
I think it is best to rip it out, its a real problem area, and REST should be no more concerned about data formats than the Java API.
I doubt anyone uses this, not even Jack. Will need to follow up with him to confirm.