cloud-fan commented on issue #26461: [SPARK-29831][SQL] Scan Hive partitioned 
table should not dramatically increase data parallelism
URL: https://github.com/apache/spark/pull/26461#issuecomment-552769026
 
 
   I agree with the problem mentioned by @viirya , but I'm not sure this config 
is the right cure. Users still need to know the big parallelism problem and set 
the config carefully.
   
   The file source config `spark.sql.files.maxPartitionBytes` is much simpler 
to use. It defines how much data you want each task to process, and mostly you 
don't need to change it for different queries.
   
   `spark.default.parallelism` doesn't really affect data source scan AFAIK. We 
do have a similar problem to set the number of reducers and we solved in with 
the recent adaptive execution work.
   
   I'm OK to have a config for hive table scan, but we should make it simple 
set.

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