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From "william zhu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-6831) The job schedule in condition task could not be correct with skewed join optimization
Date Tue, 08 Apr 2014 06:30:21 GMT

    [ https://issues.apache.org/jira/browse/HIVE-6831?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13962630#comment-13962630
] 

william zhu commented on HIVE-6831:
-----------------------------------

1. The query can be simplied like this:
Select * from 
(select   *  from   TableA  Union all select * from TableB)  a
2.  TableA and TableB is consists of other select query.  
3.  And I set the hive parameter is : 
set hive.auto.convert.join=false;
set hive.optimize.skewjoin = true;
set hive.skewjoin.key = 500000;
set hive.mapjoin.smalltable.filesize=50000000;



> The job schedule in condition task could not be correct with skewed join optimization
> -------------------------------------------------------------------------------------
>
>                 Key: HIVE-6831
>                 URL: https://issues.apache.org/jira/browse/HIVE-6831
>             Project: Hive
>          Issue Type: Bug
>          Components: Query Processor
>    Affects Versions: 0.11.0
>         Environment: Hive 0.11.0
>            Reporter: william zhu
>         Attachments: 6831.patch
>
>
> Code snippet in  ConditionalTask.java as bellow:  
>     // resolved task
>         if (driverContext.addToRunnable(tsk)) {
>           console.printInfo(tsk.getId() + " is selected by condition resolver.");
>     }
> The selected task is added into the runnable queue immediately without any dependency
checking. If the selected task is original task ,and its parent task is not being executed,
then the result will be incorrect.
> Like this:
> 1. Before skew join optimization:
> Step1 ,Step 2 <-- step 3   ( Step1 and Step2 is Step 3's parent)
> 2. after skew join optimization:
> Step1 <- Step4 (ConditionTask)<- consists of [Step3,Step10]    
> Step2 <- Step5 (ConditionTask)<- consists of [Step3,Step11]
> 3. Runing
> Step3 is selected in Step4 and Step5
> Step3 will be execute immediately after Step4 , its not correct.
> Step3 will be execute after Step5 again, its not correct either.
> 4. The correct scheduler is that step3 will be execute after step4 and step5.
> 5. So, I add a checking operate in the snippet  as bellow:
>         if (!driverContext.getRunnable().contains(tsk)) {
>           console.printInfo(tsk.getId() + " is selected by condition resolver.");
>           if(DriverContext.isLaunchable(tsk)){
>         	  driverContext.addToRunnable(tsk);
>           }
>         }
> So , that is work right for me in my enviroment. I am not sure whether it will has some
problems  in someother condition. 



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