[jira] [Created] (KYLIN-3686) Top_N metric code requires cube storage type to be ID_SHARDED_HBASE, but the Web UI defaults to ID_HBASE and provides no safeguards against storage type mismatch

["Vsevolod Ostapenko (JIRA)" <ji...@apache.org>]

Vsevolod Ostapenko created KYLIN-3686:
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             Summary: Top_N metric code requires cube storage type to be ID_SHARDED_HBASE, but the Web UI defaults to ID_HBASE and provides no safeguards against storage type mismatch
                 Key: KYLIN-3686
                 URL: https://issues.apache.org/jira/browse/KYLIN-3686
             Project: Kylin
          Issue Type: Improvement
          Components: Measure - TopN, Metadata, Web 
    Affects Versions: v2.5.0
         Environment: HDP 2.5.6, Kylin 2.5
            Reporter: Vsevolod Ostapenko


When new cube is defined via Kylin 2.5 UI, the default cube storage type is set to 0 (ID_HBASE).
Top_N metric support is currently hard coded to expect cube storage type 2 (ID_SHARDED_HBASE), and it *_does not_* check if the cube storage type is the "sharded HBASE".
UI provides no safeguards either to prevent a user from defining a cube with Top_N metric that would blow up on the cube building stage with a perplexing stack trace like the following:


{quote}2018-11-08 08:35:45,413 WARN [main] org.apache.hadoop.mapred.YarnChild: Exception running child : java.lang.IllegalArgumentException: Can't read partitions file at org.apache.hadoop.mapreduce.lib.partition.TotalOrderPartitioner.setConf(TotalOrderPartitioner.java:116) at org.apache.hadoop.util.ReflectionUtils.setConf(ReflectionUtils.java:76) at org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:136) at org.apache.hadoop.mapred.MapTask$NewOutputCollector.<init>(MapTask.java:701) at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:770) at org.apache.hadoop.mapred.MapTask.run(MapTask.java:341) at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:170) at java.security.AccessController.doPrivileged(Native Method) at javax.security.auth.Subject.doAs(Subject.java:422) at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1865) at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:164) Caused by: java.io.IOException: wrong key class: org.apache.kylin.storage.hbase.steps.RowKeyWritable is not class org.apache.hadoop.hbase.io.ImmutableBytesWritable at org.apache.hadoop.io.SequenceFile$Reader.next(SequenceFile.java:2332) at org.apache.hadoop.io.SequenceFile$Reader.next(SequenceFile.java:2384) at org.apache.hadoop.mapreduce.lib.partition.TotalOrderPartitioner.readPartitions(TotalOrderPartitioner.java:306) at org.apache.hadoop.mapreduce.lib.partition.TotalOrderPartitioner.setConf(TotalOrderPartitioner.java:88) ... 10 more
{quote}
Please, either 
** modify Top_N code to support all cube storage types (not only ID_SHARDED_HBASE), 
or 
**modify Top_N code to perform explicit check for cube storage type and raise descriptive exception, when cube storage is not the one that is expected. Plus update the UI to prevent the user from creating cube definitions that are incompatible with the storage type compatible with Top_N measure



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