DataNode Commands

The NameNode responds to heartbeats from the DataNode with, among other things, a list of commands to be executed. (See Heartbeats.)

The following commands may be sent:

• RegisterCommand
• BlockCommand
• BlockECReconstructionCommand
• BlockCachingCommand
• BlockRecoveryCommand
• FinalizerCommand (documentation lacking, but has something to do with finalizing a previous upgrade)
• KeyUpdateCommand (documentation lacking, but has something to do with updating an access key)

Hadoop also implements another command, BalancerBandwidthCommand, but it has yet to be determined whether that will be required for our implementation.