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From "Hairong Kuang (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-178) piggyback block work requests to heartbeats and move block replication/deletion startup delay from datanodes to namenode
Date Mon, 01 May 2006 18:10:46 GMT
piggyback block work requests to heartbeats and move block replication/deletion startup delay
from datanodes to namenode
------------------------------------------------------------------------------------------------------------------------

         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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