[HADOOP-178] piggyback block work requests to heartbeats and move block replication/deletion startup delay from datanodes to namenode

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.2.0
• Assignee: Hairong Kuang
• Reporter: Hairong Kuang
• Created: 02/May/06 01:09
• Updated: 08/Jul/09 16:41
• Resolved: 02/May/06 02:45

Description

Currently each datanode sends at least two messages to namenode within a heartbeat interval. One is a heartbeat message and another is block work request. By piggybacking the block work request to a heartbeat can greatly cut the number of messages between a datanode and the namenode.

Secondly each datanode waits for a configurable "StartupPeriod" before it sends a block work request in order to avoid uneccessary block replication at startup time. But if the namenode starts much later than datanodes, this scheme does not work. Furthermore, the namenode has more information to decide when to send block work to datanodes. For example, all datanodes send block reports etc. It is more resonable to move the startup delay from datanodes to the namenode