DOCS-14454 expose data size in bytes processed by sort and group in agg execution stats explain

Author: jmd-mongo

source/reference/explain-results.txt

@@ -775,6 +775,63 @@ details the indexes; e.g.:
 In previous versions of MongoDB, ``cursor.explain()`` returned the
 ``clauses`` array that detailed the indexes.
 
+.. _sort-and-group-executionStats-and-above:
+
+``$sort`` and ``$group`` Stages
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When ``explain`` is run in either  
+:ref:`executionStats <explain-method-executionStats>` or 
+:ref:`allPlansExecution <explain-method-allPlansExecution>` verbosity 
+mode, the :pipeline:`$sort` and :pipeline:`$group` stages have 
+additional output.
+
+.. list-table::
+   :header-rows: 1
+   :widths: 20 15 15 50
+
+   * - Stage
+
+     - Field
+
+     - Type
+
+     - Description
+
+   * - :pipeline:`$sort` 
+
+     - ``totalDataSizeSortedBytesEstimate``
+
+     - long
+
+     - An estimated number of bytes processed in the :pipeline:`$sort` 
+       stage.
+      
+   * - :pipeline:`$sort`
+ 
+     - ``usedDisk``
+
+     - boolean
+
+     - Whether the :pipeline:`$sort` stage wrote to disk. 
+
+   * - :pipeline:`$group`
+
+     - ``totalOutputDataSizeBytes``
+     
+     - long
+
+     - An estimate of the total size of all documents output by the 
+       :pipeline:`$group` stage in bytes.
+
+   * - :pipeline:`$group`
+ 
+     - ``usedDisk``
+
+     - boolean
+
+     - Whether the :pipeline:`$group` stage wrote to disk. 
+
 .. _explain-output-sort:
 
 Sort Stage