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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-385) Design a pluggable interface to place replicas of blocks in HDFS
Date Wed, 08 Jul 2009 09:58:14 GMT

    [ https://issues.apache.org/jira/browse/HDFS-385?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12728594#action_12728594
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dhruba borthakur commented on HDFS-385:
---------------------------------------

@Hong: * javadoc for chooseTarget contains an unused parameter : I wiill fix.
                * two versions of chooseTarget. I will make the default as you suggested.
                * asymmetry for chooseTarget which takes a list of DatanodeDescriptor: I would
like to leave it as it is because lots of code in the namenode depends on this behaviour.
Is this ok with you?

@Matei: 
  HashMap vs HashSet, not much difference as explained by Nicholas. Also, the last path does
not have any excludedNodes parameters
 * verifyBlockPlacement part of the abstract API? This method is used by fsck to verify that
the block satisfies the placement policy. 


> Design a pluggable interface to place replicas of blocks in HDFS
> ----------------------------------------------------------------
>
>                 Key: HDFS-385
>                 URL: https://issues.apache.org/jira/browse/HDFS-385
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>             Fix For: 0.21.0
>
>         Attachments: BlockPlacementPluggable.txt, BlockPlacementPluggable2.txt, BlockPlacementPluggable3.txt,
BlockPlacementPluggable4.txt, BlockPlacementPluggable4.txt
>
>
> The current HDFS code typically places one replica on local rack, the second replica
on remote random rack and the third replica on a random node of that remote rack. This algorithm
is baked in the NameNode's code. It would be nice to make the block placement algorithm a
pluggable interface. This will allow experimentation of different placement algorithms based
on workloads, availability guarantees and failure models.

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