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

["Xiao Chen (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-8046?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15328714#comment-15328714 ] 

Xiao Chen commented on HDFS-8046:
---------------------------------

Thanks [~kihwal] and all for the contribution. Great work here and on HDFS-4995 to fix NN locking issues!

Just dropping a quick note here, that increasing the default of {{DFS_CONTENT_SUMMARY_LIMIT_DEFAULT}} from 0 to 5000, plus a bug in HDFS-4995 (fixed by HDFS-8581) created a somewhat incompatible behavior on {{/}}: {{hdfs dfs -du -s /}} or {{hdfs dfs -count /}} may end up only calculate some of the dirs when the limit is reached.

I think we should backport HDFS-8581 to 2.6.x and 2.7.x to fix this.

> 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
>            Assignee: Kihwal Lee
>              Labels: 2.6.1-candidate, 2.7.2-candidate
>             Fix For: 2.6.1, 2.7.2
>
>         Attachments: HDFS-8046-branch-2.6.1.txt, HDFS-8046.v1.patch
>
>
> 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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