apache/spark — pull request #3026 by tdas (2014-10-30 23:06:36+00:00)
Title: [SPARK-4029][Streaming] Update streaming driver to reliably save and recover received block metadata on driver failures

As part of the initiative of preventing data loss on driver failure, this JIRA tracks the sub task of modifying the streaming driver to reliably save received block metadata, and recover them on driver restart.

This was solved by introducing a `ReceivedBlockTracker` that takes all the responsibility of managing the metadata of received blocks (i.e. `ReceivedBlockInfo`, and any actions on them (e.g, allocating blocks to batches, etc.). All actions to block info get written out to a write ahead log (using `WriteAheadLogManager`). On recovery, all the actions are replaying to recreate the pre-failure state of the `ReceivedBlockTracker`, which include the batch-to-block allocations and the unallocated blocks.

Furthermore, the `ReceiverInputDStream` was modified to create `WriteAheadLogBackedBlockRDD`s when file segment info is present in the `ReceivedBlockInfo`. After recovery of all the block info (through recovery `ReceivedBlockTracker`), the `WriteAheadLogBackedBlockRDD`s gets recreated with the recovered info, and jobs submitted. The data of the blocks gets pulled from the write ahead logs, thanks to the segment info present in the `ReceivedBlockInfo`.

This is still a WIP. Things that are missing here are.
- Unit test that tests the driver recovery, by killing and restarting the streaming context, and verifying all the input data gets processed.
- Cleaning up the received data write ahead log, by calling `ReceivedBlockHandler.cleanupOldBlocks`.