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From "Amareshwari Sriramadasu (JIRA)" <>
Subject [jira] [Commented] (HIVE-3952) merge map-job followed by map-reduce job
Date Wed, 27 Feb 2013 11:21:14 GMT


Amareshwari Sriramadasu commented on HIVE-3952:

Tried out the patch, when we run query like the following :

Select ....

It fails with exception :

java.lang.ClassCastException: org.apache.hadoop.hive.ql.exec.MoveTask cannot be cast to org.apache.hadoop.hive.ql.exec.MapRedTask
	at org.apache.hadoop.hive.ql.optimizer.physical.CommonJoinResolver$CommonJoinTaskDispatcher.mayBeMergeMapJoinTaskWithMapReduceTask(
	at org.apache.hadoop.hive.ql.optimizer.physical.CommonJoinResolver$CommonJoinTaskDispatcher.processCurrentTask(
	at org.apache.hadoop.hive.ql.optimizer.physical.CommonJoinResolver$CommonJoinTaskDispatcher.dispatch(
	at org.apache.hadoop.hive.ql.lib.TaskGraphWalker.dispatch(
	at org.apache.hadoop.hive.ql.lib.TaskGraphWalker.walk(
	at org.apache.hadoop.hive.ql.lib.TaskGraphWalker.startWalking(
	at org.apache.hadoop.hive.ql.optimizer.physical.CommonJoinResolver.resolve(
	at org.apache.hadoop.hive.ql.optimizer.physical.PhysicalOptimizer.optimize(
	at org.apache.hadoop.hive.ql.parse.SemanticAnalyzer.genMapRedTasks(
	at org.apache.hadoop.hive.ql.parse.SemanticAnalyzer.analyzeInternal(
	at org.apache.hadoop.hive.ql.parse.BaseSemanticAnalyzer.analyze(
	at org.apache.hadoop.hive.ql.Driver.compile(
	at org.apache.hadoop.hive.ql.Driver.compile(
	at org.apache.hadoop.hive.cli.CliDriver.processLocalCmd(
	at org.apache.hadoop.hive.cli.CliDriver.processCmd(
	at org.apache.hadoop.hive.cli.CliDriver.processLine(
	at org.apache.hadoop.hive.cli.CliDriver.main(
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(
	at java.lang.reflect.Method.invoke(
	at org.apache.hadoop.util.RunJar.main(

> merge map-job followed by map-reduce job
> ----------------------------------------
>                 Key: HIVE-3952
>                 URL:
>             Project: Hive
>          Issue Type: Improvement
>          Components: Query Processor
>            Reporter: Namit Jain
>            Assignee: Vinod Kumar Vavilapalli
>         Attachments: HIVE-3952-20130226.txt
> Consider the query like:
> select count(*) FROM
>         ( select idOne, idTwo, value FROM
>               bigTable                                       
>               JOIN                                                                
>               smallTableOne on (bigTable.idOne = smallTableOne.idOne)               
>           ) firstjoin                                                             
>             JOIN                                                                  
>             smallTableTwo on (firstjoin.idTwo = smallTableTwo.idTwo);
> where smallTableOne and smallTableTwo are smaller than
> is set to true.
> The joins are collapsed into mapjoins, and it leads to a map-only job
> (for the map-joins) followed by a map-reduce job (for the group by).
> Ideally, the map-only job should be merged with the following map-reduce job.

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