BlockCommand

BlockCommand

This command is an instruction to a DataNode regarding some blocks under its control. It tells the DataNode to do one of the following:

1. invalidate a set of indicated blocks
2. copy a set of indicated blocks to another DataNode

At a high level, this command needs to be provided a set of Blocks (to be clear, the representation of blocks in our code) and a corresponding list of DataNode targets for each block, and an ID for the pool of blocks.