Github user sun-rui commented on a diff in the pull request:
https://github.com/apache/spark/pull/12836#discussion_r62603831
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/r/MapPartitionsRWrapper.scala
---
@@ -25,6 +25,21 @@ import org.apache.spark.sql.Row
import org.apache.spark.sql.types.{BinaryType, StructField, StructType}
/**
+ * A function wrapper that applies the given R function to each partition
of each group.
+ */
+private[sql] case class MapGroupsRWrapper(
--- End diff --
Maybe can do some optimization to above idea. As it needs a buffer and
reduces the parallelism. Can improve R worker, so that multiple groups can be
passed to R worker one by one ( this way, R worker knows the group boundary),
and In the R worker, the R gapply function will be call multiple times, one for
each group. Results are flattened and merged inside the R worker.
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