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From "Erik Krogen (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-11615) FSNamesystemLock metrics can be inaccurate due to millisecond precision
Date Mon, 10 Apr 2017 20:43:41 GMT

    [ https://issues.apache.org/jira/browse/HDFS-11615?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15963464#comment-15963464
] 

Erik Krogen commented on HDFS-11615:
------------------------------------

I was thinking that the numbers are a little easier to parse/understand (for a human) and
microseconds are more indicative of the time scale for these operations but I don't have a
strong preference either way; I'm happy to adjust if there are other opinions.

> 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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