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https://issues.apache.org/jira/browse/HDFS-12143?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16091661#comment-16091661
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Daryn Sharp commented on HDFS-12143:
------------------------------------

This patch is intended to surgically fix the unnecessary performance 
degradation caused by preconditions.  The mathematical comparisons, dubious as 
they may be, are not part of the problem.

> Improve performance of getting and removing inode features
> ----------------------------------------------------------
>
>                 Key: HDFS-12143
>                 URL: https://issues.apache.org/jira/browse/HDFS-12143
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: namenode
>    Affects Versions: 2.8.0
>            Reporter: Daryn Sharp
>            Assignee: Daryn Sharp
>         Attachments: HDFS-12143.patch
>
>
> Getting a feature uses an iterator which is less performant than an indexed 
> for loop.  Feature lookups are becoming more prolific so cycles count.
> Removing a feature requires building a string for up to 3 precondition 
> checks.  The worst case of 3 is the penalty for a successful removal.



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