diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/Sink.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/Sink.scala
index 2571b59be54f..d10cd3044ecd 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/Sink.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/Sink.scala
@@ -31,8 +31,11 @@ trait Sink {
    * this method is called more than once with the same batchId (which will happen in the case of
    * failures), then `data` should only be added once.
    *
-   * Note: You cannot apply any operators on `data` except consuming it (e.g., `collect/foreach`).
+   * Note 1: You cannot apply any operators on `data` except consuming it (e.g., `collect/foreach`).
    * Otherwise, you may get a wrong result.
+   *
+   * Note 2: The method is supposed to be executed synchronously, i.e. the method should only return
+   * after data is consumed by sink successfully.
    */
   def addBatch(batchId: Long, data: DataFrame): Unit
 }