DOCSP-8628: Document new 'hello' command

Author: npentrel

source/core/replica-set-hidden-member.txt

@@ -19,7 +19,7 @@ data set but is **invisible** to client applications. Hidden members
 are good for workloads with different usage patterns from the other
 members in the :term:`replica set`. Hidden members must always be
 :ref:`priority 0 members <replica-set-secondary-only-members>` and
-so **cannot become primary**. The :method:`db.isMaster()` method does not
+so **cannot become primary**. The :method:`db.hello()` method does not
 display hidden members. Hidden members, however, **may vote** in
 :ref:`elections <replica-set-elections>`.
 

source/core/sharded-cluster-query-router.txt

@@ -135,15 +135,15 @@ Confirm Connection to ``mongos`` Instances
 ------------------------------------------
 
 To detect if the MongoDB instance that your client is connected
-to is :binary:`~bin.mongos`, use the :dbcommand:`isMaster` command. When a
-client connects to a :binary:`~bin.mongos`, :dbcommand:`isMaster` returns
+to is :binary:`~bin.mongos`, use the :dbcommand:`hello` command. When a
+client connects to a :binary:`~bin.mongos`, :dbcommand:`hello` returns
 a document with a ``msg`` field that holds the string
 ``isdbgrid``. For example:
 
 .. code-block:: javascript
 
    {
-      "ismaster" : true,
+      "isWritablePrimary" : true,
       "msg" : "isdbgrid",
       "maxBsonObjectSize" : 16777216,
       "ok" : 1,

source/includes/fact-bulkwrite-operation-batches.rst

@@ -1,7 +1,7 @@
 The number of operations in each group cannot exceed the value of
 the :limit:`maxWriteBatchSize <Write Command Batch Limit Size>` of
 the database. As of MongoDB 3.6, this value is ``100,000``.
-This value is shown in the :data:`isMaster.maxWriteBatchSize` field.
+This value is shown in the :data:`hello.maxWriteBatchSize` field.
 
 This limit prevents issues with oversized error messages. If a group
 exceeds this :limit:`limit<Write Command Operation Limit Size>`,

source/reference/command.txt

@@ -394,9 +394,13 @@ Replication Commands
 
      - Internal command that applies :term:`oplog` entries to the current data set.
 
+   * - :dbcommand:`hello`
+
+     - Displays information about this member's role in the replica set, including whether it is the primary.
+
    * - :dbcommand:`isMaster`
 
-     - Displays information about this member's role in the replica set, including whether it is the master.
+     - *Deprecated*. Use :dbcommand:`hello` instead.
 
    * - :dbcommand:`replSetAbortPrimaryCatchUp`