[jira] [Created] (KYLIN-2248) TopN merge further optimization after KYLIN-1917

["Shaofeng SHI (JIRA)" <ji...@apache.org>]

Shaofeng SHI created KYLIN-2248:
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             Summary: 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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