[jira] [Created] (SPARK-29831) Scan Hive partitioned table should not dramatically increase data parallelism

["L. C. Hsieh (Jira)" <ji...@apache.org>]

L. C. Hsieh created SPARK-29831:
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             Summary: Scan Hive partitioned table should not dramatically increase data parallelism
                 Key: SPARK-29831
                 URL: https://issues.apache.org/jira/browse/SPARK-29831
             Project: Spark
          Issue Type: Improvement
          Components: SQL
    Affects Versions: 3.0.0
            Reporter: L. C. Hsieh
            Assignee: L. C. Hsieh


Hive table scan operator reads each Hive partition as a HadoopRDD and unions all RDDs. The data parallelism of the result RDD can be dramatically increased, when reading a lot of partitions with a lot of files.

Although users can also do coalesce by themselves, this ticket proposes to add a config to limit the maximum of the data parallelism. Because:

1. end-users might not understand details and get confused by big partition number. end-users might not know why/when/where to add coalesce.
2. users need to add coalesce to each time Hive table scan. It is annoying.






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