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https://issues.apache.org/jira/browse/KYLIN-2248?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Shaofeng SHI resolved KYLIN-2248.
---------------------------------
Resolution: Fixed
> TopN merge further optimization after KYLIN-1917
> ------------------------------------------------
>
> Key: KYLIN-2248
> URL: https://issues.apache.org/jira/browse/KYLIN-2248
> Project: Kylin
> Issue Type: Improvement
> Components: Job Engine
> Reporter: Shaofeng SHI
> Assignee: Shaofeng SHI
> Fix For: v1.6.1
>
>
> After KYLIN-1917, there still be room for performance optimization when
> building a cube which has very large amount rows but the cardinality of all
> dimension are quite small.
> Then there will be much aggregation happens in building base cuboid. The
> reducer has a big pressure on CPU. With JStack we observed the CPU was spent
> on the TopNCounter.merge(), in the HashMap.get() method.
> {code}
> Thread 28679: (state = IN_JAVA)
> - java.util.HashMap.getEntry(java.lang.Object) @bci=81, line=465 (Compiled
> frame; information may be imprecise)
> - java.util.HashMap.get(java.lang.Object) @bci=11, line=417 (Compiled frame)
> -
> org.apache.kylin.measure.topn.TopNCounter.merge(org.apache.kylin.measure.topn.TopNCounter)
> @bci=117, line=174 (Compiled frame)
> -
> org.apache.kylin.measure.topn.TopNAggregator.aggregate(org.apache.kylin.measure.topn.TopNCounter)
> @bci=38, line=44 (Compiled frame)
> - org.apache.kylin.measure.topn.TopNAggregator.aggregate(java.lang.Object)
> @bci=5, line=27 (Compiled frame)
> - org.apache.kylin.measure.MeasureAggregators.aggregate(java.lang.Object[])
> @bci=42, line=76 (Compiled frame)
> -
> org.apache.kylin.engine.mr.steps.CuboidReducer.doReduce(org.apache.hadoop.io.Text,
> java.lang.Iterable, org.apache.hadoop.mapreduce.Reducer$Context) @bci=95,
> line=97 (Compiled frame)
> - org.apache.kylin.engine.mr.steps.CuboidReducer.doReduce(java.lang.Object,
> java.lang.Iterable, org.apache.hadoop.mapreduce.Reducer$Context) @bci=7,
> line=42 (Interpreted frame)
> - org.apache.kylin.engine.mr.KylinReducer.reduce(java.lang.Object,
> java.lang.Iterable, org.apache.hadoop.mapreduce.Reducer$Context) @bci=4,
> line=40 (Interpreted frame)
> -
> org.apache.hadoop.mapreduce.Reducer.run(org.apache.hadoop.mapreduce.Reducer$Context)
> @bci=22, line=171 (Interpreted frame)
> -
> org.apache.hadoop.mapred.ReduceTask.runNewReducer(org.apache.hadoop.mapred.JobConf,
> org.apache.hadoop.mapred.TaskUmbilicalProtocol,
> org.apache.hadoop.mapred.Task$TaskReporter,
> org.apache.hadoop.mapred.RawKeyValueIterator,
> org.apache.hadoop.io.RawComparator, java.lang.Class, java.lang.Class)
> @bci=119, line=627 (Interpreted frame)
> - org.apache.hadoop.mapred.ReduceTask.run(org.apache.hadoop.mapred.JobConf,
> org.apache.hadoop.mapred.TaskUmbilicalProtocol) @bci=384, line=389
> (Interpreted frame)
> - org.apache.hadoop.mapred.YarnChild$2.run() @bci=36, line=164 (Interpreted
> frame)
> -
> java.security.AccessController.doPrivileged(java.security.PrivilegedExceptionAction,
> java.security.AccessControlContext) @bci=0 (Interpreted frame)
> - javax.security.auth.Subject.doAs(javax.security.auth.Subject,
> java.security.PrivilegedExceptionAction) @bci=42, line=415 (Interpreted frame)
> -
> org.apache.hadoop.security.UserGroupInformation.doAs(java.security.PrivilegedExceptionAction)
> @bci=14, line=1709 (Interpreted frame)
> - org.apache.hadoop.mapred.YarnChild.main(java.lang.String[]) @bci=514,
> line=158 (Interpreted frame)
>
> {code}
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