datanode

type DataNode struct {
	DataPath string
	MetaPath string
	ActPath  string
	// Assigned after each format.
	// When DataNode first starts, it will perform a
	// handshake with NameNode. During this process
	// NamespaceID will be verified. (also software version
	// as described in paper, but I omit it)
	NamespaceID int
	// Persistent to disk, generated when DataNode first
	// registers with NameNode
	StorageID string
	HostName  string // e.g. thumm02
	IP        string
	Port      string
	Addr      string
	/* Each block has tow files on DataNode:
	 * 1. metadata file
	 * 2. actual data file
	 * Since DataNode will be requested with block id to
	 * retrieve data on disk, there is no need to store
	 * these meta information in memory.
	 * When a DataNode starts, it performs the following
	 * actions:
	 * 1. perform handshake with NameNode, verify NamespaceID.
	 *    NamespaceID will be reassigned after each format action.
	 * 2. register with NameNode, DataNode get a unique
	 *    StorageID, which is persistent to disk. So if
	 *    the DataNode restart with different IP, it will
	 *    still be able to work.
	 * 3. send a block report to NameNode. Report each block's
	 *    blockID, generation stamp(here I use timestamp instead)
	 *	  and block length. block report then is send periodically
	 *    to NameNode. (every hour as described in paper)
	 * 4. start sending heartbeats to NameNode. (every 3 seconds in paper)
	 *    Each heartbeat carries: total storage capacity, fraction
	 *    of storage in use, # of data transfer in progress.
	 *    Also report corrupt block to NameNode.
	 *    DataNode is considered died if NameNode hasn't received
	 *    its heartbeat for a very long time. (10 mins in paper)
	 */
	// IDList       []string
	IDToMetaData map[string]utils.MetaData
	// contains filtered or unexported fields
}

type RequestBlkArgs struct {
	BlkID string
}

type SendBlkReply struct {
	Status bool
}