Document db.collection.mapReduce return values

source/reference/command/mapReduce.txt

@@ -87,8 +87,8 @@ mapReduce
    :start-after: start-finalize
    :end-before: end-finalize
 
-Examples
---------
+Map-Reduce Examples
+-------------------
 
 In the :program:`mongo` shell, the :method:`db.collection.mapReduce()`
 method is a wrapper around the :dbcommand:`mapReduce` command. The
@@ -101,14 +101,112 @@ For more information and examples, see the
 :doc:`Map-Reduce </core/map-reduce>` page and
 :doc:`/tutorial/perform-incremental-map-reduce`.
 
-.. seealso::
+.. _mapreduce-output:
 
-   - :doc:`/tutorial/troubleshoot-map-function`
+Output
+------
 
-   - :doc:`/tutorial/troubleshoot-reduce-function`
+If you set the :ref:`out <mapReduce-out-cmd>` parameter to write the
+output of the operation to a collection, the :dbcommand:`mapReduce`
+command returns a document in the following form:
 
-   - :method:`db.collection.mapReduce()`
+.. code-block:: javascript
 
-   - :doc:`/core/aggregation`
+   {
+       "result" : "map_reduce_example",
+       "timeMillis" : <milliseconds>,
+       "counts" : {
+           "input" : <int>,
+           "emit" : <int>,
+           "reduce" : <int>,
+           "output" : <int>
+       },
+       "ok" : 1,
+   }
+
+If you set the :ref:`out <mapReduce-out-cmd>` parameter to output results
+inline, the :dbcommand:`mapReduce` command returns a document in the
+following form:
+
+.. code-block:: javascript
+
+   {
+       "results" : [
+          {
+             "_id" : "abc123",
+             "value" : 0
+          },
+          {
+             "_id" : "ijk021",
+             "value" : 0
+          },
+          {
+             "_id" : "stu523",
+             "value" : null
+          },
+          {
+             "_id" : "xyz321",
+             "value" : 0
+          }
+       ],
+       "timeMillis" : <milliseconds>,
+       "counts" : {
+          "input" : <int>,
+          "emit" : <int>,
+          "reduce" : <int>,
+          "output" : <int>
+       },
+       "ok" : 1
+   }
+
+.. data:: mapReduce.result
+
+   For output sent to a collection, this value includes the collection
+   name where the :dbcommand:`mapReduce` command wrote the results. If the
+   :ref:`out <mapReduce-out-cmd>` parameter specified a database and
+   collection name, the value includes both names.
+
+   For output written inline, the result includes an array with the
+   ``_id`` and ``value`` fields for each result.
+
+.. data:: mapReduce.timeMillis
+
+   The command execution time in milliseconds.
+
+.. data:: mapReduce.counts
+
+   Counts of function calls generated by the :dbcommand:`mapReduce` command.
+
+.. data:: mapReduce.counts.input
+
+   The number of times the :dbcommand:`mapReduce` command called the ``input`` function.
+
+.. data:: mapReduce.counts.emit
+
+   The number of times the :dbcommand:`mapReduce` command called the ``emit`` function.
+
+.. data:: mapReduce.counts.reduce
+
+   The number of times the :dbcommand:`mapReduce` command called the ``reduce`` function.
+
+.. data:: mapReduce.counts.output
+
+   The number of output values produced.
+
+.. data:: mapReduce.ok
+
+   A value of ``1`` indicates the :dbcommand:`mapReduce` command ran
+   successfully. A value of ``0`` indicates an error.
+
+Additional Information
+----------------------
+
+- :doc:`/tutorial/troubleshoot-map-function`
+
+- :doc:`/tutorial/troubleshoot-reduce-function`
+
+- :method:`db.collection.mapReduce()`
+
+- :doc:`/core/aggregation`
 
 .. slave-ok

source/reference/method/db.collection.mapReduce.txt

@@ -67,16 +67,26 @@ db.collection.mapReduce()
 
 .. include:: /includes/examples-map-reduce.rst
 
-For more information and examples, see the
-:doc:`Map-Reduce </core/map-reduce>` page and
-:doc:`/tutorial/perform-incremental-map-reduce`.
+Output
+------
 
-.. seealso::
+For more information about the output the :dbcommand:`mapReduce` command
+generates if you set the :ref:`out <mapReduce-out-cmd>` parameter to send
+results to a collection, see the :ref:`Output <mapReduce-output>` section
+of the :dbcommand:`mapReduce` page.
 
-   - :doc:`/tutorial/troubleshoot-map-function`
+Additional Information
+----------------------
 
-   - :doc:`/tutorial/troubleshoot-reduce-function`
+- :doc:`/tutorial/troubleshoot-map-function`
 
-   - :dbcommand:`mapReduce` command
+- :doc:`/tutorial/troubleshoot-reduce-function`
+
+- :dbcommand:`mapReduce` command
+
+- :doc:`/core/aggregation`
+
+- :doc:`Map-Reduce </core/map-reduce>`
+
+- :doc:`/tutorial/perform-incremental-map-reduce`
 
-   - :doc:`/core/aggregation`