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https://issues.apache.org/jira/browse/HADOOP-5724?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12708445#action_12708445
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dhruba borthakur commented on HADOOP-5724:
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> NN does not remove a replica from blocksMap immediately when scheduling to 
> delete the replica due to over-replication/

any reason why the NN does not remove a replica from the block map at the time 
of sending the block-delete request to the datanode when it is trying to reduce 
over-replication?

> Datanode should report deletion of blocks to Namenode explicitly
> ----------------------------------------------------------------
>
>                 Key: HADOOP-5724
>                 URL: https://issues.apache.org/jira/browse/HADOOP-5724
>             Project: Hadoop Core
>          Issue Type: Bug
>            Reporter: Suresh Srinivas
>            Assignee: Suresh Srinivas
>             Fix For: 0.21.0
>
>         Attachments: blockdel.patch, blockdel.patch
>
>
> Currently datanode notifies namenode newly added blocks and the blocks that 
> are corrupt. There is no explicit message from the datanode to the namenode 
> to indicate the deletion of blocks. Block reports from the datanode is the 
> only way for the namenode to learn about the deletion of blocks at a 
> datanode. With the addition of explicit request to indicate to block 
> deletion, block report interval (which is currently 1 hour) can be increased 
> to a longer duration. This reduces load on both namenode and datanodes.
>  

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