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https://issues.apache.org/jira/browse/HDFS-8873?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Daniel Templeton updated HDFS-8873:
-----------------------------------
Attachment: HDFS-8873.001.patch
Here's a patch to add a time-based throttle. The changes are a little large
because I had to first make the scanner throttlable. I also took the liberty
of fleshing out the javadocs. The throttling approach is explained in the
comments and javadocs.
> 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
>
>
> 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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