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https://issues.apache.org/jira/browse/HDFS-11907?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16034021#comment-16034021
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Andrew Wang commented on HDFS-11907:
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Thanks for the reply [~vagarychen]. Just thought I'd mention the other class in
case there was potential for code sharing.
Could you expand a little on why caching is necessary here? As Kihwal said, df
is normally pretty cheap, so I'm curious why we need to do this. We could also
get possibly the same outcome by increasing the monitorHealth check interval
from 1s to 5s.
> 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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