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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Created] (MAPREDUCE-7128) LocalJobRunner may fail due to metrics name collision
Date Sat, 11 Aug 2018 00:38:00 GMT
Todd Lipcon created MAPREDUCE-7128:

             Summary: LocalJobRunner may fail due to metrics name collision
                 Key: MAPREDUCE-7128
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-7128
             Project: Hadoop Map/Reduce
          Issue Type: Bug
            Reporter: Todd Lipcon

Running Hive in local mode, I got the following failure:
	Caused by: org.apache.hadoop.metrics2.MetricsException: Metrics source LocalJobRunnerMetrics-1090927800
already exists!
		at org.apache.hadoop.metrics2.lib.DefaultMetricsSystem.newSourceName(DefaultMetricsSystem.java:152)
		at org.apache.hadoop.metrics2.lib.DefaultMetricsSystem.sourceName(DefaultMetricsSystem.java:125)
		at org.apache.hadoop.metrics2.impl.MetricsSystemImpl.register(MetricsSystemImpl.java:229)
		at org.apache.hadoop.mapred.LocalJobRunnerMetrics.create(LocalJobRunnerMetrics.java:46)

It seems that it tries to generate a unique metrics source name using a random 32-bit integer.
When running some longer-lived program that runs many separate jobs (such as HS2) this can
easily collide. https://en.wikipedia.org/wiki/Birthday_attack has some tables for the probabilities.

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