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https://issues.apache.org/jira/browse/HDFS-7174?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14525040#comment-14525040
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Hadoop QA commented on HDFS-7174:
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| (x) *{color:red}-1 overall{color}* |
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|| Vote || Subsystem || Runtime || Comment ||
| {color:red}-1{color} | patch |   0m  0s | The patch command could not apply 
the patch during dryrun. |
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|| Subsystem || Report/Notes ||
| Patch URL | 
http://issues.apache.org/jira/secure/attachment/12672576/HDFS-7174.new.patch |
| Optional Tests | javadoc javac unit findbugs checkstyle |
| git revision | trunk / f1a152c |
| Console output | 
https://builds.apache.org/job/PreCommit-HDFS-Build/10703/console |


This message was automatically generated.

> Support for more efficient large directories
> --------------------------------------------
>
>                 Key: HDFS-7174
>                 URL: https://issues.apache.org/jira/browse/HDFS-7174
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Kihwal Lee
>            Assignee: Kihwal Lee
>            Priority: Critical
>         Attachments: HDFS-7174.new.patch, HDFS-7174.patch, HDFS-7174.patch
>
>
> When the number of children under a directory grows very large, insertion 
> becomes very costly.  E.g. creating 1M entries takes 10s of minutes.  This is 
> because the complexity of an insertion is O\(n\). As the size of a list 
> grows, the overhead grows n^2. (integral of linear function).  It also causes 
> allocations and copies of big arrays.



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