DOCS-5392 : nscanned/keysExamined "end" check update

Author: ravindk89

source/release-notes/3.2.txt

@@ -670,6 +670,44 @@ addition to the numbers corresponding to the BSON types.
 :method:`db.collection.distinct()` method. For more information, see
 :method:`db.collection.explain()`.
 
+``keysExamined`` Statistic Corrected
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The :method:`explain()` method's output in ``executionStats`` or 
+``allPlansExecution`` mode contains the ``keysExamined`` statistic 
+(``nScanned`` in MongoDB 2.4 and 2.6), representing the number of 
+index keys examined during index scans. It is also reported in the 
+logs and the system profiler.
+
+For the ``IXSCAN`` query execution stage, ``keysExamined`` is the total number 
+of in-range and out-of-range keys that are examined in the process of the 
+index scan. If the index scan consists of a single contiguous range of keys, 
+generally only in-range keys need to be examined. If the index bounds 
+translate to several key ranges, the index scan execution process may examine 
+out-of-range keys in order to skip from the end of one range to the beginning 
+of the next.
+
+For example, given a collection with an index on field ``x`` with 100 unique 
+values between 1 and 100, the following performs a find operation with the 
+:method:`explain()` method in ``executionStats`` mode:
+
+.. code-block:: javascript
+
+   db.keys.find( { x : $in : [ 3, 4, 50, 74, 75, 90 ] } ).explain( "executionStats" )
+   
+The query will scan keys ``3`` and ``4``. It will then scan the key ``5``, 
+detect that it is out of range, and skip to the next key ``50``. 
+
+The query scans keys 3, 4, 5, 50, 51, 74, 75, 76, 90, and 91. Keys 
+``5``, ``51``, ``76``, and ``91`` are out-of-range keys that are still 
+examined. 
+
+Prior to 3.2, the last out-of-range key ``91`` was not counted due to an 
+accounting error. ``keysExamined`` returned ``9``.
+
+As of 3.2, that last out-of-range key is included in the ``keysExamined`` 
+value. ``keysExamined`` now returns ``10``.
+
 .. _3.2-relnotes-2dsphere-index:
 
 Geospatial Optimization