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From "Tom White (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3799) Design a pluggable interface to place replicas of blocks in HDFS
Date Fri, 19 Jun 2009 15:04:07 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3799?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12721805#action_12721805
] 

Tom White commented on HADOOP-3799:
-----------------------------------

Hi Dhruba,

A couple more comments:

> BlockPlacementInterface#chooseTarget(). Make excludedNodes a List<DatanodeDescriptor>.
Implementations may choose to turn it into a map if they need to, but for the interface, it
should just be a list, shouldn't it?

I think you missed this change.

I'm not convinced that ReplicationPolicyChooser is needed. Couldn't we add a static method
(e.g. getInstance()) to BlockPlacementPolicy to construct a BlockPlacementPolicy from the
dfs.block.replicator.classname property? We can add an overloaded chooseTarget() method to
BlockPlacementPolicy which doesn't take a chosenNodes argument (BTW this is misspelt as "choosenNodes"
in BlockPlacementPolicy).

> Design a pluggable interface to place replicas of blocks in HDFS
> ----------------------------------------------------------------
>
>                 Key: HADOOP-3799
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3799
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: dfs
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>         Attachments: BlockPlacementPluggable.txt, BlockPlacementPluggable2.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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