viirya 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-552774504 > 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. Because the default parallelism affects `maxSplitBytes`: https://github.com/apache/spark/blob/053dd858d38e6107bc71e0aa3a4954291b74f8c8/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/FilePartition.scala#L86-L95 IIUC, `spark.sql.files.maxPartitionByte` and `spark.default.parallelism` both affect the used split byte and so final parallelism in scan. Maybe we can also rely on `maxSplitBytes` in Hive Scan and decide parallelism?
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