Github user marmbrus commented on a diff in the pull request:
https://github.com/apache/spark/pull/16758#discussion_r98775275
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/KeyValueGroupedDataset.scala ---
@@ -219,6 +219,160 @@ class KeyValueGroupedDataset[K, V] private[sql](
}
/**
+ * ::Experimental::
+ * (Scala-specific)
+ * Applies the given function to each group of data, while using an
additional keyed state.
+ * For each unique group, the function will be passed the group key and
an iterator that contains
+ * all of the elements in the group. The function can return an object
of arbitrary type, and
+ * optionally update or remove the corresponding state. The returned
object will form a new
+ * [[Dataset]].
+ *
+ * This function can be applied on both batch and streaming Datasets.
With a streaming dataset,
+ * this function will be once for each in every trigger. For each key,
the updated state from the
+ * function call in a trigger will be the state available in the
function call in the next
--- End diff --
Any updates to the state will be stored and passed to the user given
function in subsequent batches when executed as a Streaming Query.
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