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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