[GitHub] [spark] wangyum commented on pull request #29709: [WIP][SPARK-32842] Support dynamic partition pruning hint

[GitBox <gi...@apache.org>]

wangyum commented on pull request #29709:
URL: https://github.com/apache/spark/pull/29709#issuecomment-690328789


   > Can't we just do this automatically by applying the "would this be small
   enough to broadcast" criterion instead of looking at the "is this actually
   selected for broadcast"?
   
   First of all, this is a `SortMergeJoin`. To use DPP, you need to disable `spark.sql.optimizer.dynamicPartitionPruning.reuseBroadcastOnly`. But disabling `spark.sql.optimizer.dynamicPartitionPruning.reuseBroadcastOnly` may affect other Join.
   
   Second, the statistics of the plan are usually inaccurate, which makes us unable to determine whether it is suitable for broadcasting in the plan phase.
   
   So, I think it’s most appropriate to add hint.
   


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