[jira] [Commented] (KYLIN-4567) Improve TopN merge performance in MR engine

["ASF GitHub Bot (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KYLIN-4567?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17153329#comment-17153329 ] 

ASF GitHub Bot commented on KYLIN-4567:
---------------------------------------

zzcclp commented on a change in pull request #1259:
URL: https://github.com/apache/kylin/pull/1259#discussion_r451362075



##########
File path: core-metadata/src/main/java/org/apache/kylin/measure/topn/TopNCounter.java
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@@ -43,8 +43,10 @@
 public class TopNCounter<T> implements Iterable<Counter<T>>, java.io.Serializable {
 
     public static final int EXTRA_SPACE_RATE = 50;
+    public static final int EXTRA_SORT_RATE = 10;

Review comment:
       It's better to add a property for this parameter, and set to a default value.




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> Improve TopN merge performance in MR engine
> -------------------------------------------
>
>                 Key: KYLIN-4567
>                 URL: https://issues.apache.org/jira/browse/KYLIN-4567
>             Project: Kylin
>          Issue Type: Improvement
>          Components: Measure - TopN
>            Reporter: Guangxu Cheng
>            Assignee: Guangxu Cheng
>            Priority: Major
>
> We have a cube that needs to calculate the TOPN of 13 columns. The number of data source is only 500k. But, the cubing job always fail when building base cuboid.
> we found that the map task always killed by the ApplicationMaster due to time out
> {noformat}
> ERROR-[-10001]-[MR]:[Mr Task Timeout]:[AttemptID:attempt_1591996262448_229922_m_000000_1 Timed out after 3600 secs!] ERROR-[-10015]-[MR]:[Container Exit Accidentally]:[Container killed by the ApplicationMaster. Container killed on request. Exit code is 143 Container exited with a non-zero exit code 143 ]
> {noformat}
> the stack information as below:
> {noformat}
> "SpillThread" #35 daemon prio=5 os_prio=0 tid=0x00007f9a89771800 nid=0x133a2 runnable [0x00007f9a56e3f000]
>    java.lang.Thread.State: RUNNABLE
>         at java.util.LinkedList.toArray(LinkedList.java:1052)
>         at java.util.List.sort(List.java:477)
>         at java.util.Collections.sort(Collections.java:175)
>         at org.apache.kylin.measure.topn.TopNCounter.sortAndRetain(TopNCounter.java:96)
>         at org.apache.kylin.measure.topn.TopNCounter.merge(TopNCounter.java:183)
>         at org.apache.kylin.measure.topn.TopNAggregator.aggregate(TopNAggregator.java:44)
>         at org.apache.kylin.measure.topn.TopNAggregator.aggregate(TopNAggregator.java:27)
>         at org.apache.kylin.measure.MeasureAggregators.aggregate(MeasureAggregators.java:83)
>         at org.apache.kylin.engine.mr.steps.CuboidReducer.doReduce(CuboidReducer.java:108)
>         at org.apache.kylin.engine.mr.steps.CuboidReducer.doReduce(CuboidReducer.java:44)
>         at org.apache.kylin.engine.mr.KylinReducer.reduce(KylinReducer.java:77)
>         at org.apache.hadoop.mapreduce.Reducer.run(Reducer.java:171)
>         at org.apache.hadoop.mapred.Task$NewCombinerRunner.combine(Task.java:1688)
>         at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.sortAndSpill(MapTask.java:1645)
>         at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.access$900(MapTask.java:884)
>         at org.apache.hadoop.mapred.MapTask$MapOutputBuffer$SpillThread.run(MapTask.java:1540)
> {noformat}
> From the stack information, we found that sorting takes a lot of time. After merge another counter into this counter, need to re-sort this counter. Maybe we can reduce the frequency of sorting



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