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Date: Mon, 6 Jul 2009 18:25:14 -0700 (PDT)
From: "Matei Zaharia (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Subject: [jira] Commented: (HDFS-385) Design a pluggable interface to place
 replicas of blocks in HDFS
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    [ https://issues.apache.org/jira/browse/HDFS-385?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12727863#action_12727863 ] 

Matei Zaharia commented on HDFS-385:
------------------------------------

Hey Dhruba, a couple of quick questions:
* Why is excludedNodes a HashMap? A HashSet should perform at least as well and use less memory.
* Why is verifyBlockPlacement part of the abstract API? It seems to be something that can be checked regardless of the replication policy as long as you know the network topology. Is this just in case the policy does not want to use the existing NetworkTopology class?

> 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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