[jira] [Commented] (HDFS-8046) Allow better control of getContentSummary

["Kihwal Lee (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-8046?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14392972#comment-14392972 ] 

Kihwal Lee commented on HDFS-8046:
----------------------------------

I will post a patch that we applied in our systems. Many clusters have been running with it for some time now.

> Allow better control of getContentSummary
> -----------------------------------------
>
>                 Key: HDFS-8046
>                 URL: https://issues.apache.org/jira/browse/HDFS-8046
>             Project: Hadoop HDFS
>          Issue Type: Bug
>            Reporter: Kihwal Lee
>
> On busy clusters, users performing quota checks against a big directory structure can affect the namenode performance. It has become a lot better after HDFS-4995, but as clusters get bigger and busier, it is apparent that we need finer grain control to avoid long read lock causing throughput drop.
> Even with unfair namesystem lock setting, a long read lock (10s of milliseconds) can starve many readers and especially writers. So the locking duration should be reduced, which can be done by imposing a lower count-per-iteration limit in the existing implementation.  But HDFS-4995 came with a fixed amount of sleep between locks. This needs to be made configurable, so that {{getContentSummary()}} doesn't get exceedingly slow.



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