[SPARK-7139] Allow received block metadata to be saved to WAL and recovered on driver failure

• Type: Sub-task
• Status: Resolved
• Priority: Blocker
• Resolution: Fixed
• Fix Version/s: 1.4.0
• Component/s: DStreams
• Target Version/s: 1.4.0
• Assignee: Tathagata Das
• Reporter: Tathagata Das
• Created: 24/Apr/15 22:19
• Updated: 01/Aug/15 06:03
• Resolved: 05/May/15 08:46

Description

The received API allows arbitrary metadata to be added for each block. However that information is not saved in the WAL as part of the block information in the driver.

To fix this, the following needs to be done.

1. Forward the metadata to the ReceivedBlockTracker in the driver.
2. ReceivedBlockTracker saves the metadata and recovers it on restart.

However there is one tricky thing. The ReceivedBlockTracker WAL is enabled only when `spark.streaming.receiver.writeAheadLog.enable = true`. This means that only when receiver WAL is enabled is the driver WAL enabled. This is not desired as the one may want to save and recovered block metadata information (especially information like Kafka offsets or Kinesis sequence numbers) that can be used to recover data without actually saving the data to the receiver WAL. So we have to always enable the tracker WAL.

3. Always enable the ReceivedBlockTracker WAL. However, make sure that the WriteAheadLogBackedBlockRDD skips block lookup after restart as the blocks are obviously gone.

Issue Links

• is depended upon by: SPARK-9217 Update Kinesis Receiver to record sequence numbers
• links to: [Github] Pull Request #5732 (tdas)