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From "Erik Krogen (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (MAPREDUCE-6919) ShuffleMetrics.ShuffleConnections Gauge Metric Rises Infinitely
Date Tue, 25 Jul 2017 23:50:00 GMT

     [ https://issues.apache.org/jira/browse/MAPREDUCE-6919?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Erik Krogen updated MAPREDUCE-6919:
-----------------------------------
    Attachment: MAPREDUCE-6919.test.patch

Attaching a unit test which reproduces the issue. Had to refactor {{ShuffleHandler.Shuffle}}
a little to get the test to work nicely.

> ShuffleMetrics.ShuffleConnections Gauge Metric Rises Infinitely
> ---------------------------------------------------------------
>
>                 Key: MAPREDUCE-6919
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-6919
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: mrv2
>            Reporter: Erik Krogen
>         Attachments: mapred_ShuffleMetrics_ShuffleConnections.png, MAPREDUCE-6919.test.patch
>
>
> We recently noticed that the mapred.ShuffleMetrics.ShuffleConnections metric rises indefinitely
(see attached graph), despite supposedly being a gauge measuring the number of currently open
connections:
> {code:title=ShuffleHandler.java}
>     @Metric("# of current shuffle connections")
>         MutableGaugeInt shuffleConnections;
> {code}
> It seems this is because the metric is incremented once for each map file sent, but decremented
once for each request. Thus a request which fetches multiple map files permanently increments
shuffleConnections by (mapsFetched - 1).



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