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https://issues.apache.org/jira/browse/HDFS-11907?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16032274#comment-16032274
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Arpit Agarwal commented on HDFS-11907:
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Thanks for updating the patch [~vagarychen]. A few minor comments:
# Typo: availabeSpaceTimeStamp --> availableSpaceTimeStamp
# Typo: DF_STALE_THREASHOLD_MS --> DF_STALE_THRESHOLD_MS
# Looks like the two threshold values were swapped from v2 to v3 patch. I think
the v2 values were better.
# getAvailabeSpaceTimeStamp can be package private. Also the new constructor.
# in the test case, can you add an assert for the {{// first call guarantees an
update}} e.g.
{code}
// first call guarantees an update
long val0 = nb.getAvailabeSpaceTimeStamp();
volume.isResourceAvailable();
long val1 = nb.getAvailabeSpaceTimeStamp();
assertEquals(val0 + 5000, val1);
timer.advance(2000);
{code}
Looks good otherwise!
> 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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