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From "Zhe Zhang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-11615) FSNamesystemLock metrics can be inaccurate due to millisecond precision
Date Wed, 12 Apr 2017 23:24:41 GMT

    [ https://issues.apache.org/jira/browse/HDFS-11615?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15966800#comment-15966800
] 

Zhe Zhang commented on HDFS-11615:
----------------------------------

bq. "XxxNanosAvgTime" is reasonable but I'm hesitant to emit a metric called "XxxNanosNumOps"...
DataNode already has multiple metrics named with that convention. E.g. {{FlushNanosAvgTime}}.
So I guess that makes it less awkward :)

> FSNamesystemLock metrics can be inaccurate due to millisecond precision
> -----------------------------------------------------------------------
>
>                 Key: HDFS-11615
>                 URL: https://issues.apache.org/jira/browse/HDFS-11615
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: hdfs
>    Affects Versions: 2.7.4
>            Reporter: Erik Krogen
>            Assignee: Erik Krogen
>         Attachments: HDFS-11615.000.patch
>
>
> Currently the {{FSNamesystemLock}} metrics created in HDFS-10872 track the lock hold
time using {{Timer.monotonicNow()}}, which has millisecond-level precision. However, many
of these operations hold the lock for less than a millisecond, making these metrics inaccurate.
We should instead use {{System.nanoTime()}} for higher accuracy.



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