[jira] Commented: (HADOOP-5479) NameNode should not send empty block replication request to DataNode

["Konstantin Shvachko (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-5479?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12682410#action_12682410 ] 

Konstantin Shvachko commented on HADOOP-5479:
---------------------------------------------

+1 on all changes.

Little thing:
{{else}} clause in {{DatanodeDescriptor.BlockQueue.poll()}} can be removed.

> NameNode should not send empty block replication request to DataNode
> --------------------------------------------------------------------
>
>                 Key: HADOOP-5479
>                 URL: https://issues.apache.org/jira/browse/HADOOP-5479
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: dfs
>            Reporter: Hairong Kuang
>            Assignee: Hairong Kuang
>            Priority: Critical
>             Fix For: 0.19.2, 0.20.0, 0.21.0
>
>         Attachments: numTransfers.patch
>
>
> On our production clusters, we occasionally see that NameNode sends an empty block replication request to DataNode on  every heartbeat, thus blocking this DataNode from replicating or deleting any block.
> This is partly caused by DataNode sending a wrong number of replications in progress which will be fixed by HADOOP-5465. There is also a flaw at the NameNode side. NameNode should not interpret the number of replications in progress as the number of targets since replication is done through a pipeline. It also should make sure that no empty replication request is sent to DataNode.

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