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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