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From "Dmytro Molkov (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1431) Balancer should work with the logic of BlockPlacementPolicy
Date Thu, 30 Sep 2010 23:25:35 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1431?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12916732#action_12916732

Dmytro Molkov commented on HDFS-1431:

I like the idea in general. The only concern is that the BlockPlacementPolicy originally used
to work only inside of the NameNode itself and thus had direct access to the namenode datastructures.
This method will have to act as if it works outside of the NameNode which is different form
all other methods.

> Balancer should work with the logic of BlockPlacementPolicy
> -----------------------------------------------------------
>                 Key: HDFS-1431
>                 URL: https://issues.apache.org/jira/browse/HDFS-1431
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: balancer
>    Affects Versions: 0.22.0
>            Reporter: Scott Chen
>            Assignee: Scott Chen
>             Fix For: 0.22.0
>         Attachments: HDFS-1431.txt
> Currently Balancer does not obtain information from BlockPlacementPolicy so it can transfer
the blocks without checking with BlockPlacementPolicy.
> This causes the policy break after balancing the cluster.
> There are some new policies proposed in HDFS-1094 and MAPREDUCE-1831 in which the block
placement follows some pattern.
> The pattern can be broken by Balancer.
> I propose that we add the following method in BlockPlacementPolicy:
> {code}
>   abstract public boolean canBeMoved(String fileName, Block block,
>     DatanodeInfo source, DatanodeInfo destination);
> {code}
> And make Balancer use it in
> {code}
>   private boolean isGoodBlockCandidate(Source source,
>       BalancerDatanode target, BalancerBlock block)
> {code}
> What do you think?

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