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From "Andrew Wang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-11907) NameNodeResourceChecker should avoid calling df.getAvailable too frequently
Date Tue, 06 Jun 2017 20:37:18 GMT

    [ https://issues.apache.org/jira/browse/HDFS-11907?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16039589#comment-16039589
] 

Andrew Wang commented on HDFS-11907:
------------------------------------

Hi, sorry for the slow reply, was out on Friday and Monday,

If we haven't confirmed the problem, I'd support adding additional logs or metrics for better
debugging, but making behavior changes seems premature. Is there a metric for the {{df}} call
that we can look at to confirm slowness? Other host-level statistics that we can check?

> NameNodeResourceChecker should avoid calling df.getAvailable too frequently
> ---------------------------------------------------------------------------
>
>                 Key: HDFS-11907
>                 URL: https://issues.apache.org/jira/browse/HDFS-11907
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Chen Liang
>            Assignee: Chen Liang
>         Attachments: HDFS-11907.001.patch, HDFS-11907.002.patch, HDFS-11907.003.patch,
HDFS-11907.004.patch
>
>
> Currently, {{HealthMonitor#doHealthChecks}} invokes {{NameNode#monitorHealth}} which
ends up invoking {{NameNodeResourceChecker#isResourceAvailable}}, at the frequency of once
per second by default. And NameNodeResourceChecker#isResourceAvailable invokes {{df.getAvailable();}}
every time it is called.
> Since available space information should rarely be changing dramatically at the pace
of per second. A cached value should be sufficient. i.e. only try to get the updated value
when the cached value is too old. otherwise simply return the cached value. This way df.getAvailable()
gets invoked less.
> Thanks [~arpitagarwal] for the offline discussion.



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