DOCS 15330 opportunistic reads - Backport v5.0 (#1862)

* DOCS-15330 opportunisticSecondaryTargeting (#1824)

* DOCS-15330 Adds server parameter

* DOCS-15330 Updates description

* DOCS-15330 Updates notice

* DOCS-15330 Updates metadata

* DOCS-15330 Updates notice

* DOCS-15330 Fixes per Joe

* DOCS-15330 Fixes per Joe

* DOCS-15330 Fixes per Vojislav

* DOCS-15330 Sets version per Jira

Author: kennethdyer

source/reference/parameters.txt

@@ -2778,6 +2778,41 @@ Sharding Parameters
       - :serverstatus:`shardedIndexConsistency` metrics returned by the
         :dbcommand:`serverStatus` command.
 
+.. parameter:: opportunisticSecondaryTargeting
+
+   .. versionadded:: 5.0.10
+
+   *Type*: boolean
+
+   *Default*: ``false``
+
+   |mongos-only|
+
+   Determines whether ``mongos`` performs opportunistic reads against
+   replica sets.
+
+   When this parameter is set to ``true``, :program:`mongos` directs secondary 
+   reads to secondaries with active connections. It sends the request to the 
+   first secondary that accepts the connection. When this parameter is set to 
+   ``false``, :program:`mongos` holds secondary reads until it can establish 
+   a connection to a specific secondary, (except in the case of 
+   :ref:`hedged reads <read-preference-hedged-read>`).
+
+   .. note:: 
+
+      Under certain workloads, opportunistic reads may trigger the 
+      opening of unnecessary connections from :program:`mongos` to 
+      :program:`mongod` and reduce overall performance. 
+      This parameter should not be enabled unless your application has 
+      a specific need for the feature.
+
+   For example, to set ``opportunisticSecondaryTargeting`` during startup:
+
+   .. code-block:: bash
+
+      mongos --setParameter opportunisticSecondaryTargeting=true
+
+
 .. parameter:: shardedIndexConsistencyCheckIntervalMS
 
    *New in version 4.4 (and 4.2.6).*