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https://issues.apache.org/jira/browse/HDFS-11634?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16060195#comment-16060195
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Konstantin Shvachko commented on HDFS-11634:
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Good job measuring this, [~zhz]. Thanks.
The main outcome here I think is substantial reduction in NN lock holding time
for internal (housekeeping) load.
> Optimize BlockIterator when iterating starts in the middle.
> -----------------------------------------------------------
>
> Key: HDFS-11634
> URL: https://issues.apache.org/jira/browse/HDFS-11634
> Project: Hadoop HDFS
> Issue Type: Improvement
> Affects Versions: 2.6.5
> Reporter: Konstantin Shvachko
> Assignee: Konstantin Shvachko
> Fix For: 2.9.0, 2.7.4, 3.0.0-alpha4, 2.8.2
>
> Attachments: HDFS-11634.001.patch, HDFS-11634.002.patch,
> HDFS-11634.003.patch, HDFS-11634.004.patch, HDFS-11634.006.patch,
> HDFS-11634-branch-2.7.006.patch, HDFS-11643.005.patch, Screen Shot 2017-06-21
> at 1.39.21 PM.png
>
>
> {{BlockManager.getBlocksWithLocations()}} needs to iterate blocks from a
> randomly selected {{startBlock}} index. It creates an iterator which points
> to the first block and then skips all blocks until {{startBlock}}. It is
> inefficient when DN has multiple storages. Instead of skipping blocks one by
> one we can skip entire storages. Should be more efficient on average.
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