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From "Tsz Wo (Nicholas), SZE (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-1765) Block Replication should respect under-replication block priority
Date Fri, 02 Dec 2011 00:06:40 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1765?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13161322#comment-13161322
] 

Tsz Wo (Nicholas), SZE commented on HDFS-1765:
----------------------------------------------

Hi Uma, the proposed solution sounds good.  Having an index for each priority will solve the
problem.

BTW, chooseUnderReplicatedBlocks(..) and replIndex in BlockManager should be moved to UnderReplicatedBlocks.
                
> Block Replication should respect under-replication block priority
> -----------------------------------------------------------------
>
>                 Key: HDFS-1765
>                 URL: https://issues.apache.org/jira/browse/HDFS-1765
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: name-node
>    Affects Versions: 0.23.0
>            Reporter: Hairong Kuang
>            Assignee: Hairong Kuang
>             Fix For: 0.24.0
>
>         Attachments: HDFS-1765.pdf, underReplicatedQueue.pdf
>
>
> Currently under-replicated blocks are assigned different priorities depending on how
many replicas a block has. However the replication monitor works on blocks in a round-robin
fashion. So the newly added high priority blocks won't get replicated until all low-priority
blocks are done. One example is that on decommissioning datanode WebUI we often observe that
"blocks with only decommissioning replicas" do not get scheduled to replicate before other
blocks, so risking data availability if the node is shutdown for repair before decommission
completes.

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