DOCSP-38784: Sharded cluster retries (mongodb#539)

Author: norareidy

source/whats-new.txt

@@ -56,6 +56,15 @@ Deprecations in 5.1
   deployment, see :manual:`Release Notes </release-notes>` in the {+mdb-server+}
   manual.
 
+.. _java-behavioral-changes-5.1:
+
+Behavioral Changes in 5.1
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+- When a sharded cluster operation is unsuccessful, the {+driver-short+} avoids selecting
+  the same ``mongos`` server for operation retry attempts if other ``mongos`` servers are
+  available.  
+
 .. _version-5.0:
 
 What's New in 5.0