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From "Hairong Kuang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-5724) Datanode should report deletion of blocks to Namenode explicitly
Date Tue, 12 May 2009 17:17:45 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-5724?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12708516#action_12708516
] 

Hairong Kuang commented on HADOOP-5724:
---------------------------------------

> 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?

One more reason: because there is a delay between scheduling a replica to remove and the replica
getting removed at a datanode, keeping the replica in blocksMap could avoid placing the block
on this datanode if ever an under-replication happens to occur.  That why we had HADOOP-4643
instead of HADOOP-4540.

> 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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