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

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

Arthur created SPARK-35008:
------------------------------

             Summary: 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


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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