piggyback block work requests to heartbeats and move block replication/deletion
startup delay from datanodes to namenode
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Key: HADOOP-178
URL: http://issues.apache.org/jira/browse/HADOOP-178
Project: Hadoop
Type: Improvement
Components: dfs
Reporter: Hairong Kuang
Assigned to: Hairong Kuang
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
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