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https://issues.apache.org/jira/browse/HDFS-11907?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16033960#comment-16033960
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Chen Liang commented on HDFS-11907:
-----------------------------------
Thanks [~andrew.wang] for the comments! We prefer not to use it here though
because:
1. the change of this JIRA is about maintaining *available space* value, while
DFCachingGetSpaceUsed is to get *used space*. So we will have to make further
modification to this class (or create new) if we want to use it.
2. seems that each instance of this class will use an extra background thread
that periodically updates the value, which seems a bit overkill to me.
But if you do think it is better to use DFCachingGetSpaceUsed, I will try to
update with another patch.
> 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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