Connection Pools

On this page

Overview
Create a Connection Pool
Configure a Connection Pool
Additional Information

Overview

In this guide, you can learn about how the Java driver 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 Java driver. When your application requests a connection to MongoDB, the Java driver 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 Java driver.

Create a Connection Pool

Every MongoClient instance has a built-in connection pool for each server in your MongoDB topology. Connection pools open sockets on demand to support concurrent MongoDB operations in your multi-threaded application.

The maxPoolSize option sets the maximum size of each connection pool, which defaults to 100. If the number of in-use connections to a server reaches the value of maxPoolSize, the next request to that server will wait until a connection becomes available.

Each MongoClient instance opens two more sockets per server in your MongoDB topology for monitoring the server's state.

Configure a Connection Pool

You can specify settings for your connection pool using either a connection string or by passing a MongoClientSettings object to the MongoClients.create() method.

The following code creates a client with a maximum connection pool size of 50. Select the Connection String or MongoClientSettings tab to see the corresponding syntax:

ConnectionString connectionString = "mongodb://<host>:<port>/?maxPoolSize=50"
MongoClient mongoClient = MongoClients.create(connectionString)

The following are connection string settings you can use to configure your connection pool:

Setting	Description
`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: `0`
`maxPoolSize`	Maximum number of connections opened in the pool. When the connection pool reaches the maximum number of connections, new connections wait up until to the value of `waitQueueTimeoutMS`. 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`
`waitQueueTimeoutMS`	Maximum wait time in milliseconds that an operation can wait for a connection to become available. A value of `0` means there is no limit. Default: `120000` (120 seconds)

To learn more about connection string options, see the Connection Options guide.

MongoClient mongoClient = MongoClients.create(
    MongoClientSettings.builder().applyConnectionString(
        new ConnectionString("<your connection string>"))
    .applyToConnectionPoolSettings(builder ->
        builder.maxSize(50))
    .build());

For more information on configuring you connection pool by using a MongoClientSettings object see the Connection Pool Settings section of the Specify MongoClient Settings guide.

Additional Information

For more information on using a connection pool, see the Connection Pool documentation in the Server manual.

MongoDB Java Driver