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https://issues.apache.org/jira/browse/HDFS-7967?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15812791#comment-15812791
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Allen Wittenauer commented on HDFS-7967:
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Sorry. :(
I tried hard to make hyphens as separators work (and in some cases they do),
but other cases were just not reliable enough, even when cross referencing a
list of valid branches. (.e.g, is HADOOP-6671-HADOOP-6671-2.patch a patch for
the HADOOP-6671 branch or the HADOOP-6671-2 branch? The YARN-5355-branch-2
branch brings a whole new level of hurt...)
> Reduce the performance impact of the balancer
> ---------------------------------------------
>
> Key: HDFS-7967
> URL: https://issues.apache.org/jira/browse/HDFS-7967
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: namenode
> Affects Versions: 2.0.0-alpha
> Reporter: Daryn Sharp
> Assignee: Daryn Sharp
> Priority: Critical
> Attachments: HDFS-7967-branch-2.8.patch, HDFS-7967-branch-2.patch,
> HDFS-7967.branch-2-1.patch, HDFS-7967.branch-2.001.patch,
> HDFS-7967.branch-2.8-1.patch, HDFS-7967.branch-2.8.001.patch
>
>
> The balancer needs to query for blocks to move from overly full DNs. The
> block lookup is extremely inefficient. An iterator of the node's blocks is
> created from the iterators of its storages' blocks. A random number is
> chosen corresponding to how many blocks will be skipped via the iterator.
> Each skip requires costly scanning of triplets.
> The current design also only considers node imbalances while ignoring
> imbalances within the nodes's storages. A more efficient and intelligent
> design may eliminate the costly skipping of blocks via round-robin selection
> of blocks from the storages based on remaining capacity.
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