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https://issues.apache.org/jira/browse/HDFS-8873?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14791470#comment-14791470
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Hadoop QA commented on HDFS-8873:
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| (x) *{color:red}-1 overall{color}* |
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|| Vote || Subsystem || Runtime || Comment ||
| {color:red}-1{color} | pre-patch |  15m 49s | Findbugs (version ) appears to 
be broken on trunk. |
| {color:green}+1{color} | @author |   0m  0s | The patch does not contain any 
@author tags. |
| {color:green}+1{color} | tests included |   0m  0s | The patch appears to 
include 1 new or modified test files. |
| {color:red}-1{color} | javac |   2m  3s | The patch appears to cause the 
build to fail. |
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|| Subsystem || Report/Notes ||
| Patch URL | 
http://issues.apache.org/jira/secure/attachment/12756379/HDFS-8873.003.patch |
| Optional Tests | javadoc javac unit findbugs checkstyle |
| git revision | trunk / 0832b38 |
| Console output | 
https://builds.apache.org/job/PreCommit-HDFS-Build/12499/console |


This message was automatically generated.

> throttle directoryScanner
> -------------------------
>
>                 Key: HDFS-8873
>                 URL: https://issues.apache.org/jira/browse/HDFS-8873
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: datanode
>    Affects Versions: 2.7.1
>            Reporter: Nathan Roberts
>            Assignee: Daniel Templeton
>         Attachments: HDFS-8873.001.patch, HDFS-8873.002.patch, 
> HDFS-8873.003.patch
>
>
> The new 2-level directory layout can make directory scans expensive in terms 
> of disk seeks (see HDFS-8791) for details. 
> It would be good if the directoryScanner() had a configurable duty cycle that 
> would reduce its impact on disk performance (much like the approach in 
> HDFS-8617). 
> Without such a throttle, disks can go 100% busy for many minutes at a time 
> (assuming the common case of all inodes in cache but no directory blocks 
> cached, 64K seeks are required for full directory listing which translates to 
> 655 seconds) 



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