GH-33830: Clarify handling of Null values in REE encoding (#33831)

zagto · westonpace · web-flow · commit b9d116276a5b · 2023-01-23T10:43:29.000-05:00
* Closes: #33830 Lead-authored-by: Tobias Zagorni <tobias@zagorni.eu> Co-authored-by: zagto <tobias@zagorni.eu> Co-authored-by: Weston Pace <weston.pace@gmail.com> Signed-off-by: Matt Topol <zotthewizard@gmail.com>
diff --git a/docs/source/format/Columnar.rst b/docs/source/format/Columnar.rst
@@ -815,6 +815,9 @@ A run must have have a length of at least 1. This means the values in the
 run ends array all are positive and in strictly ascending order. A run end cannot be
 null.
 
+The REE parent has no validity bitmap, and it's null count field should always be 0.
+Null values are encoded as runs with the value null.
+
 As an example, you could have the following data: ::
 
     type: Float32
@@ -824,7 +827,7 @@ In Run-end-encoded form, this could appear as:
 
 ::
 
-    * Length: 7, Null count: 2
+    * Length: 7, Null count: 0
     * Child Arrays:
 
       * run_ends (Int32):
