DOCS-14167 ReplicaSetMatching default to disabled

Author: npentrel

source/reference/command/connPoolStats.txt

@@ -86,6 +86,7 @@ The command returns the output of the following form:
       "totalAvailable" : <num>,
       "totalCreated" : <num>,
       "totalRefreshing" : <num>,
+      "replicaSetMatchingStrategy" : <string>,
       "pools" : {
          "NetworkInterfaceTL-TaskExecutorPool-0" : {
             "poolInUse" : <num>,
@@ -300,7 +301,6 @@ The command returns the output of the following form:
          "signature" : <document>
       },
       "operationTime" : <timestamp>
-      
    }
 
 Output
@@ -331,6 +331,38 @@ Output
    members of the :term:`sharded cluster` or :term:`replica set` that
    are currently being refreshed.
 
+.. data:: connPoolStats.replicaSetMatchingStrategy
+
+   .. versionadded:: 5.0 (*Also available starting in 4.4.5 and 4.2.13*)
+
+   On a :binary:`~bin.mongos` instance, this value reports the policy
+   used by the instance to determine the minimum size limit of its
+   connection pools to nodes within replica sets.
+
+   On a :binary:`~bin.mongod` instance, this value reports the policy
+   used by the instance to determine the minimum size limit of its
+   connection pools to nodes within *other* replica sets.
+
+   The policy for :binary:`~bin.mongos` and :binary:`~bin.mongod` can be
+   set with the :parameter:`ShardingTaskExecutorPoolReplicaSetMatching`
+   parameter.
+
+   .. note::
+
+      If the :parameter:`ShardingTaskExecutorPoolReplicaSetMatching` is
+      set to ``"automatic"``, the
+      :data:`~connPoolStats.replicaSetMatchingStrategy` still describes
+      the actual policy being used, not ``"automatic"``. To find the
+      value of the
+      :parameter:`ShardingTaskExecutorPoolReplicaSetMatching`, use
+      :dbcommand:`getParameter` which returns the value of the server
+      parameter:
+
+      .. code-block:: javascript
+
+         db.adminCommand( { getParameter : 1, "ShardingTaskExecutorPoolReplicaSetMatching" : 1 } )
+
+
 .. data:: connPoolStats.numClientConnection
 
    Reports the number of active and stored outgoing **synchronous**

source/reference/parameters.txt

@@ -3019,46 +3019,97 @@ Sharding Parameters
 .. parameter:: ShardingTaskExecutorPoolReplicaSetMatching
 
    .. versionadded:: 4.2
+   .. versionchanged:: 5.0 (*Also starting in 4.4.5 and
+      4.2.13*)
 
    Type: string
 
-   Default: "matchPrimaryNode"
+   Default: "automatic"
 
    |both|
-   
-   The policy that determines the minimum size limit of the
-   :binary:`~bin.mongos` instance's connection pools to the sharded
-   cluster's replica set secondaries.
+
+   On a :binary:`~bin.mongos` instance, this parameter sets the policy
+   that determines the minimum size limit of its connection pools to
+   nodes within replica sets.
+
+   On a :binary:`~bin.mongod` instance, this parameter sets the policy
+   that determines the minimum size limit of its connection pools to
+   nodes within *other* replica sets.
+
+   Note that this parameter only manages connections for operations that
+   are directly related to user requests and CRUD operations.
 
    Available values are:
-   
+
    .. list-table::
       :header-rows: 1
       :widths: 15 85
-      
+
       * - Matching Policy
         - Description
 
-      * - ``"matchPrimaryNode"`` (Default)
-      
-        - For each replica set in the sharded cluster (specifically,
-          shard replica set and config servers), the minimum size limit
-          of the :binary:`~bin.mongos` instance's connection pool to
-          each secondary of that replica set is equal to the size of its
-          connection pool to the primary.
+      * - ``"automatic"`` (Default)
+
+        - Starting in 5.0 (and 4.4.5 and 4.2.13), ``"automatic"`` is the
+          new default value.
+
+          When set for a :binary:`~bin.mongos`, the instance follows the
+          behavior specified for the ``"matchPrimaryNode"`` option.
 
-          In case of primary stepdown, ``matchPrimaryNode`` ensures
+          When set for a :binary:`~bin.mongod`, the instance follows the
+          behavior specified for the ``"disabled"`` option.
+
+          .. note::
+
+             If the
+             :parameter:`ShardingTaskExecutorPoolReplicaSetMatching` is
+             set to ``"automatic"``, the
+             :data:`~connPoolStats.replicaSetMatchingStrategy` still
+             describes the actual policy being used, not
+             ``"automatic"``. To find the value of the
+             :parameter:`ShardingTaskExecutorPoolReplicaSetMatching`,
+             use :dbcommand:`getParameter` which returns the value of
+             the server parameter.
+
+      * - ``"matchPrimaryNode"``
+
+        - When set for a :binary:`~bin.mongos`, the minimum size limit
+          of the instance's connection pool to each secondary of a
+          replica set in the sharded cluster (specifically, shard
+          replica set and config servers) is equal to the size of its
+          connection pool to that replica set's primary.
+
+          When set for a :binary:`~bin.mongod`, the minimum size limit
+          of the instance's connection pool to each secondary of
+          another replica set in the sharded cluster (specifically,
+          shard replica set and config servers) is equal to the size of
+          its connection pool to that replica set's primary.
+
+          .. warning::
+
+             If multiple shard servers in your topology can experience a
+             rapid influx of cross-shard operations, do not set this
+             option on your :binary:`~bin.mongod` instances.
+
+          In case of a primary stepdown, ``matchPrimaryNode`` ensures
           that any secondary that becomes the primary can handle the
           current level of primary reads and writes.
 
       * - ``"matchBusiestNode"``
 
-        - For each replica set in the sharded cluster (specifically,
-          shard replica set and config servers), the minimum size limit
-          of the :binary:`~bin.mongos` instance's connection pool to
-          each member of that replica set is equal to the largest among
-          the active connections counts to the primary and each
-          secondary members.
+        - When set for a :binary:`~bin.mongos`, the instance's minimum
+          size limit of the connection pool to each member of a replica
+          set in the sharded cluster (specifically, shard replica set
+          and config servers) is equal to the largest among the active
+          connection counts to the primary and each secondary member of
+          that replica set.
+
+          When set for a :binary:`~bin.mongod`, the instance's minimum
+          size limit of the connection pool to each member of another
+          replica set in the sharded cluster (specifically, shard
+          replica set and config servers) is equal to the largest among
+          the active connection counts to the primary and each
+          secondary member of that replica set.
 
           With ``"matchBusiestNode"``, :binary:`~bin.mongos` maintains
           enough connections to each secondary to handle the current
@@ -3068,26 +3119,32 @@ Sharding Parameters
 
       * - ``"disabled"``
 
-        - For each replica set in the sharded cluster (specifically,
-          shard replica set and config servers), the minimum number of
-          connections in the :binary:`~bin.mongos` instance's connection
-          pool to each secondary is equal to the
-          :parameter:`ShardingTaskExecutorPoolMinSize`.
+        - When set for a :binary:`~bin.mongos`, the instance's minimum
+          number of connections in the instance's connection pool to
+          each node of a replica set in the sharded clusterv
+          (specifically, shard replica set and config servers) is equal
+          to the :parameter:`ShardingTaskExecutorPoolMinSize`.
+
+          When set for a :binary:`~bin.mongod`, the instance's minimum
+          number of connections in the instance's connection pool to
+          each node of another replica set in the sharded cluster
+          (specifically, shard replica set and config servers) is equal
+          to the :parameter:`ShardingTaskExecutorPoolMinSize`.
 
    The following example sets the
    :parameter:`ShardingTaskExecutorPoolReplicaSetMatching` to
-   ``"matchBusiestNode"`` during startup:
+   ``"automatic"`` during startup:
 
    .. code-block:: sh
 
-      mongod --setParameter ShardingTaskExecutorPoolReplicaSetMatching="matchBusiestNode"
+      mongod --setParameter ShardingTaskExecutorPoolReplicaSetMatching="automatic"
 
    During runtime, you can also set the parameter with the
    :dbcommand:`setParameter` command:
 
    .. code-block:: javascript
 
-      db.adminCommand( { setParameter: 1,  ShardingTaskExecutorPoolReplicaSetMatching: "matchBusiestNode" } )
+      db.adminCommand( { setParameter: 1,  ShardingTaskExecutorPoolReplicaSetMatching: "automatic" } )
 
 .. parameter:: taskExecutorPoolSize
 

source/release-notes/5.0.txt

@@ -152,6 +152,17 @@ shell method) include additional information about the status of ongoing
 resharding operations for the resharding coordinator and the
 donor and recipient shards.
 
+``mongos`` / ``mongod`` Connection Pool
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Starting in MongoDB 5.0 (also available starting in 4.4.5 and 4.2.13),
+MongoDB adds the parameter option ``"automatic"`` as the new default for
+the :parameter:`ShardingTaskExecutorPoolReplicaSetMatching`. When set
+for a :binary:`~bin.mongos`, the instance follows the behavior specified
+for the ``"matchPrimaryNode"`` option. When set for a
+:binary:`~bin.mongod`, the instance follows the behavior specified for
+the ``"disabled"`` option.
+
 .. _5.0-rel-notes-security:
 
 Security