[jira] [Created] (MAPREDUCE-6919) ShuffleMetrics.ShuffleConnections Gauge Metric Rises Infinitely

["Erik Krogen (JIRA)" <ji...@apache.org>]

Erik Krogen created MAPREDUCE-6919:
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             Summary: 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


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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