I've read the source code and it seems to be impossible, but I'd like to confirm it.
It is a very useful feature. For example, I need to store the state of DStream into my database, in order to recovery them from next redeploy. But I only need to save the updated ones. Save all keys into database is a lot of waste. Through the source code, I think it could be add easily: StateDStream can get prevStateRDD so that it can make a diff. Is there any chance to add this as an API of StateDStream? If so, I can work on this feature. If not possible, is there any work around or hack to do this by myself?
