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DOCSP-51325: Connection pools
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‎source/connect/connection-pools.txt‎

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:depth: 2
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:class: singlecol
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.. facet::
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:name: genre
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:values: reference
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.. _kotlin-sync-connection-pool-settings:
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Overview
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--------
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.. TODO
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In this guide, you can learn about how the {+driver-short+} uses connection pools to manage
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connections to a MongoDB deployment. You can specify connection pool settings
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in your application to configure this behavior.
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A connection pool is a cache of open database connections maintained by the {+driver-short+}.
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When your application requests a connection to MongoDB, the driver retrieves
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a connection from the pool, performs operations, and returns the connection
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to the pool for reuse.
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Connection pools help reduce application latency and the number of times the driver
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creates new connections.
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Create a Connection Pool
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------------------------
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Every ``MongoClient`` instance has a built-in connection pool for each server
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in your MongoDB topology. Connection pools open sockets on demand to support
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concurrent MongoDB operations in your multi-threaded application.
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The ``maxPoolSize`` option sets the maximum size of each connection pool, which
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defaults to 100. If the number of in-use connections to a server reaches the
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value of ``maxPoolSize``, the next request to that server waits until a
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connection becomes available.
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Each ``MongoClient`` instance opens two more sockets per server in your MongoDB
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topology to monitor the server's state.
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Configure a Connection Pool
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---------------------------
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You can specify settings for your connection pool by using either a connection
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string or a ``MongoClientSettings`` object.
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Select the :guilabel:`Connection String` or :guilabel:`MongoClientSettings` tab to
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see the corresponding syntax:
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.. tabs::
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.. tab:: Connection String
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:tabid: uri
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The following table describes connection pool options that you can set
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in your connection string:
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.. list-table::
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:widths: 25,75
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:header-rows: 1
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* - Option
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- Description
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* - ``maxConnecting``
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- Sets the maximum number of connections a pool may establish
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concurrently.
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*Default:* ``2``
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* - ``maxIdleTimeMS``
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- Sets the maximum number of milliseconds that a connection can
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remain idle in the pool before it is removed and closed.
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*Default:* ``0``
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* - ``maxPoolSize``
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- Sets the maximum number of connections that can be open in a pool. If an
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operation needs a new connection while the connection pool has
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the maximum number of open connections, the operation
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waits for a new connection to open. To limit this
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waiting time, use the single timeout setting. To learn more,
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see the :ref:`kotlin-sync-csot` guide.
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*Default:* ``100``
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* - ``minPoolSize``
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- Sets the minimum number of connections that can be open in a pool.
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The value of ``minPoolSize`` must be less than
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the value of ``maxPoolSize``.
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*Default*: ``0``
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* - ``maxLifeTimeMS``
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- Sets the maximum amount of time, in milliseconds, the driver
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can continue to use a pooled connection before closing the
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connection. A value of ``0`` indicates that there is no upper bound on
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how long the driver can keep a pooled connection open.
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*Default*: ``0``
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To learn more about these options, see the `ConnectionString
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<{+core-api+}/ConnectionString.html>`__ API documentation.
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.. tab:: MongoClientSettings
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:tabid: MongoClient
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To specify connection pool settings in a ``MongoClientSettings`` object,
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chain the ``applyToConnectionPoolSettings()`` method to the ``MongoClientSettings`` builder.
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The following table describes the setter methods you can use inside ``applyToConnectionPoolSettings()``
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to configure the connection pool:
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.. list-table::
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:widths: 40 60
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:header-rows: 1
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* - Method
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- Description
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* - ``addConnectionPoolListener()``
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- Adds a listener for connection pool-related events.
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* - ``applyConnectionString()``
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- Applies the settings from a ``ConnectionString`` object.
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* - ``applySettings()``
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- Uses the connection pool settings specified in a
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``ConnectionPoolSettings`` object.
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* - ``maintenanceFrequency()``
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- Sets the frequency for running connection pool maintenance jobs.
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* - ``maintenanceInitialDelay()``
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- Sets the time to wait before running the first maintenance job
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on the connection pool.
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* - ``maxConnectionIdleTime()``
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- Sets the maximum time a connection can be idle before it's closed.
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* - ``maxConnectionLifeTime()``
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- Sets the maximum time a pooled connection can be open before it's
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closed.
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* - ``maxSize()``
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- Sets the maximum number of connections that can be open in a pool.
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*Default*: ``100``
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* - ``maxWaitTime()``
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- Sets the maximum time to wait for an available connection.
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*Default*: ``2`` minutes
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* - ``minSize()``
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- Sets the minimum number of connections that can be open in a pool.
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*Default*: ``0``
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To learn more about these methods, see the `applyToConnectionPoolSettings()
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<{+core-api+}/MongoClientSettings.Builder.html#applyToConnectionPoolSettings(com.mongodb.Block)>`__
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API documentation.
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Example
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~~~~~~~
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The following example shows how to create a connection pool that
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has maximum size of ``50`` connections.
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Select the :guilabel:`Connection String` or :guilabel:`MongoClientSettings` tab to
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see the corresponding syntax:
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.. tabs::
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.. tab:: Connection String
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:tabid: uri
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.. literalinclude:: /includes/connect/connection-pools.kt
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:start-after: start-uri-option
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:end-before: end-uri-option
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:language: kotlin
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:dedent:
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.. tab:: MongoClientSettings
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:tabid: MongoClient
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.. literalinclude:: /includes/connect/connection-pools.kt
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:start-after: start-client-settings
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:end-before: end-client-settings
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:language: kotlin
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:dedent:
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Additional Information
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----------------------
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To learn more about using a connection pool, see the
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:manual:`Connection Pool </administration/connection-pool-overview>`
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entry in the {+mdb-server+} manual.

‎source/includes/connect/connection-pools.kt‎

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import com.mongodb.ConnectionString
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import com.mongodb.MongoClientSettings
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import com.mongodb.ServerAddress
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import com.mongodb.ServerApi
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import com.mongodb.ServerApiVersion
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import com.mongodb.kotlin.client.MongoClient
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fun main() {
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// start-uri-option
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val uri = "mongodb://<host>:<port>/?maxPoolSize=50"
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val client = MongoClient.create(uri)
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// end-uri-option
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// start-client-settings
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val mongoClient = MongoClient.create(
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MongoClientSettings.builder()
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.applyConnectionString(ConnectionString("<connection string>"))
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.applyToConnectionPoolSettings { builder ->
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builder.maxSize(50)
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}
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.build()
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)
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// end-client-settings
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}

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