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From "Kihwal Lee (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-11907) NameNodeResourceChecker should avoid calling df.getAvailable too frequently
Date Thu, 01 Jun 2017 15:44:04 GMT

    [ https://issues.apache.org/jira/browse/HDFS-11907?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16033177#comment-16033177
] 

Kihwal Lee commented on HDFS-11907:
-----------------------------------

The {{statfs()}} call is not expensive, but I agree that the current calling frequency is
a bit excessive.  Since it is one of conditions that can trigger a NN failover, any change
here will affect the failure detection latency. The increase from max 1 second latency to
max 5 seems acceptable.

> 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
>
>
> 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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