[jira] [Comment Edited] (SPARK-29265) Window orderBy causing full-DF orderBy

["Florentino Sainz (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-29265?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16938989#comment-16938989 ] 

Florentino Sainz edited comment on SPARK-29265 at 9/26/19 9:54 PM:
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Sorry, ima test again... I'm seeing something that doesn't match in my test case.

I thought the cause was because it triggered a global sort, but plan is similar different to the one generated when ordering by another column, someone knows why a similar Window+orderBy (ordering by one of the partitionBy columns) tanked my performance and only used one executor?


was (Author: fsainz):
Sorry, ima test again... I'm seeing something that doesn't match in my test case.

I thought the cause was because it triggered a global sort, but plan is similar different to the one generated when ordering by another column, someone knows why a similar Window+orderBy tanked my performance and only used one executor?

> Window orderBy causing full-DF orderBy 
> ---------------------------------------
>
>                 Key: SPARK-29265
>                 URL: https://issues.apache.org/jira/browse/SPARK-29265
>             Project: Spark
>          Issue Type: Bug
>          Components: Spark Core
>    Affects Versions: 2.3.0, 2.4.3, 2.4.4
>         Environment: Any
>            Reporter: Florentino Sainz
>            Priority: Minor
>         Attachments: Test.scala, TestSpark.zip
>
>
> Hi,
>  
> I had this problem in "real" environments and also made a self-contained test ( [^Test.scala] attached).
> Having this Window definition:
> {code:scala}
> val myWindow = Window.partitionBy($"word").orderBy("word") 
> val filt2 = filtrador.withColumn("avg_Time", avg($"number").over(myWindow)){code}
>  
> As a user, I would expect either:
> 1- Error/warning (because trying to sort on one of the columns of the window partitionBy)
> 2- A mostly-useless operation which just orders the rows (which have the same value on word) inside each Window but doesn't affect performance too much.
>  
> Currently what I see:
> *When I use "myWindow" in any DataFrame, somehow that Window.orderBy is performing a global orderBy on the whole DataFrame. Similar to dataframe.orderBy("word").*
> *In my real environment, my program just didn't finish in time/crashed thus causing my program to be very slow or crash (because as it's a global orderBy, it will just go to one executor).*
>  
> In the test I can see how all elements of my DF are in a single partition (side-effect of the global orderBy) 
>  
> Full Code showing the error (see how the mapPartitions shows 99 rows in one partition) attached in Test.scala, sbt project (src and build.sbt) attached too in TestSpark.zip.



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