DOCSP-47023 Connection pools

source/connect/connection-options/connection-pools.txt

@@ -4,4 +4,158 @@
 Connection Pools
 ================
 
-.. TODO
+.. contents:: On this page
+   :local:
+   :backlinks: none
+   :depth: 2
+   :class: singlecol
+
+.. facet::
+   :name: genre
+   :values: reference
+
+Overview
+--------
+
+In this guide, you can learn about how the {+driver-short+} uses connection
+pools to manage connections to a MongoDB deployment and how you can configure
+connection pool settings in your application.
+
+A connection pool is a cache of open database connections maintained by the
+{+driver-short+}. When your application requests a connection to MongoDB, the
+{+driver-short+} seamlessly gets a connection from the pool, performs
+operations, and returns the connection to the pool for reuse.
+
+Connection pools help reduce application latency and the number of times new
+connections are created by {+driver-short+}.
+
+.. _golang-faq-connection-pool:
+
+Create a Connection Pool
+------------------------
+
+Every ``Client`` instance has a built-in connection pool for each server in your
+MongoDB topology. If you do not configure the ``minPoolSize`` option, connection
+pools open sockets on demand. These sockets support concurrent MongoDB
+operations, or `goroutines <https://go.dev/tour/concurrency/1>`__, in
+your application.
+
+Each ``Client`` instance opens two more sockets per server in your MongoDB
+topology for monitoring the server's state. 
+
+For example, a client connected to a three-node replica set opens six monitoring
+sockets. If the application uses the default setting for ``maxPoolSize`` and
+only queries the primary (default) node, then there can be at most ``106`` open
+sockets and ``100`` connections in the connection pool. If the application uses
+a :ref:`read preference <golang-read-pref>` to query the secondary nodes, their
+pools also grow and there can be ``306`` total connections.
+
+Create a client once for each process, and reuse it for all operations. Avoid
+creating a new client for each request, as this is inefficient.
+
+Configure a Connection Pool
+---------------------------
+
+You can specify settings for your connection pool either by using a connection
+string with the ``options.Client().ApplyURI()`` method.
+
+The following are connection string settings you can use to configure your
+connection pool:
+
+.. list-table::
+   :widths: 25,75                                                          
+   :header-rows: 1
+
+   * - Setting
+     - Description
+
+   * - ``maxPoolSize``
+
+     - Maximum number of connections opened in the pool. If an operation needs a
+       new connection while the connection pool has ``maxPoolSize`` connections
+       open, the new operation waits for a new connection to open. To limit this
+       waiting time, use the single timeout setting.
+
+       *Default:* ``100`` 
+
+   * - ``minPoolSize``
+
+     - Minimum number of connections opened in the pool. The value of
+       ``minPoolSize`` must be less than the value of ``maxPoolSize``.
+
+       *Default*: ``0``
+
+   * - ``maxConnecting``
+
+     - Maximum number of connections a pool may establish concurrently.
+
+       *Default:* ``2``
+
+   * - ``maxIdleTimeMS``
+
+     - The maximum number of milliseconds that a connection can remain idle in
+       the pool before being removed and closed.
+
+       *Default:* ``None`` (no limit)
+
+   * - ``waitQueueTimeoutMS```
+
+     - Specifies the maximum wait time in milliseconds that a thread can wait
+       for a connection to become available.
+
+       *Default*: ``0`` (no limit)
+
+The following code creates a client with a maximum connection pool size of
+``50``, a minimum pool size of ``10``, and a maximum idle time of
+``30000`` milliseconds (30 seconds):
+
+.. literalinclude:: /includes/connect/connection-pools-uri.go
+   :language: go
+   :start-after: start-connection-pool-uri
+   :end-before: end-connection-pool-uri
+   :dedent:
+
+Optimize Connection Pools
+-------------------------
+
+Connection pools are rate-limited such that each connection pool can only create,
+at maximum, the value of ``maxConnecting`` connections in parallel at any time.
+Any new goroutine stops waiting in the following cases:
+
+- One of the existing goroutines finishes creating a connection, or an existing
+  connection is checked back into the pool.
+- The driver's ability to reuse existing connections improves due to rate-limits
+  on connection creation.
+
+The driver does not limit the number of operations that can wait for sockets to
+become available and it is the application's responsibility to limit the size of
+its pool to bound queuing during a load spike. Operations can wait for any length of time
+unless you define the ``waitQueueTimeoutMS`` option.
+
+An operation that waits more than the length of time defined by
+``waitQueueTimeoutMS`` for a socket raises a connection error. Use this option
+if it is more important to bound the duration of operations during a load spike
+than it is to complete every operation.
+
+Disconnecting
+-------------
+
+When you call ``Client.Disconnect()`` from any goroutine, the driver closes all
+idle sockets and closes all sockets in use as they are returned to the pool.
+
+Additional Information
+----------------------
+
+For more information on using a connection pool, see the :manual:`Connection
+Pool </administration/connection-pool-overview>` documentation in the Server
+manual. 
+
+API Documentation
+~~~~~~~~~~~~~~~~~
+
+To learn more about any of the methods or types discussed in this
+guide, see the following API documentation:
+
+- `Client <{+api+}/mongo#Client>`__
+- `ClientOptions <{+api+}/mongo/options#ClientOptions>`__
+- `Client.Diconnect() <{+api+}/mongo#Client.Disconnect>`__

source/includes/connect/connection-pools-uri.go

@@ -0,0 +1,28 @@
+package main
+
+import (
+	"context"
+	"log"
+
+	"go.mongodb.org/mongo-driver/v2/mongo"
+	"go.mongodb.org/mongo-driver/v2/mongo/options"
+)
+
+func main() {
+	//start-connection-pool-uri
+	// Connection string with connection pool options
+	uri := "mongodb://localhost:27017/?maxPoolSize=50&minPoolSize=10&maxIdleTimeMS=30000"
+
+	// Creates a new client and connect to the server
+	client, err := mongo.Connect(options.Client().ApplyURI(uri))
+	if err != nil {
+		log.Fatal(err)
+	}
+	//end-connection-pool-uri
+
+	defer func() {
+		if err = client.Disconnect(context.TODO()); err != nil {
+			log.Fatal(err)
+		}
+	}()
+}