[jira] [Commented] (SPARK-35008) Spark hangs after on doing multiple unions

["Hyukjin Kwon (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-35008?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17318629#comment-17318629 ] 

Hyukjin Kwon commented on SPARK-35008:
--------------------------------------

Let's interact with mailing list for questions before filing it as an issue. I am sure you can have a better answer there.

> Spark hangs after on doing multiple unions
> ------------------------------------------
>
>                 Key: SPARK-35008
>                 URL: https://issues.apache.org/jira/browse/SPARK-35008
>             Project: Spark
>          Issue Type: Question
>          Components: SQL
>    Affects Versions: 3.1.1
>            Reporter: Arthur
>            Priority: Major
>
> I'm trying to union a list of {{Dataset<Rows>}} like so:
>  
> {{}}
> {code:java}
> totalSet = sparkSession.emptyDataset(RowEncoder.apply(schema)); 
> for(var currentDataset : datasetList)
>      totalSet = totalSet.union(currentDataset);
> totalSet.show(10000,false);
> {code}
> {{}}
> There's about 160 datasets in datasetList. totalSet should only have 1k rows at the end of the loop. However, spark gets stuck here in this loop. If I union just 1 dataset from datasetList it works just fine. I thought doing unions ought to be a O(1) operation, but that doesn't seem to be the case. Does anyone know why this code hangs?



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