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https://issues.apache.org/jira/browse/SPARK-35008?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17318630#comment-17318630
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Hyukjin Kwon commented on SPARK-35008:
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The reason is most likely the plans being grown too much, and the analysis gets
slowed down or stuck somewhere.
> 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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