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https://issues.apache.org/jira/browse/HDFS-1431?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12916735#action_12916735
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Scott Chen commented on HDFS-1431:
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Dmytro: That's a good point.
How about this? We can create an interface like
{code}
interface BlockMovePolicy {
boolean canBeMoved(...);
}
{code}
And make BlockPlacementPolicy implement the interface.
In Balancer, we use only this interface.
> 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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