Connection Pool Monitoring

Overview

This guide shows you how to use the Rust driver to monitor the driver's connection pool. A connection pool is a set of open Transmission Control Protocol (TCP) connections that your driver maintains with a MongoDB instance. Connection pools help reduce the number of new connections your application needs to create, which might make your application run faster.

You can use information about changes to your connection pool in your application, or you can monitor the connection pool to learn more about how the driver uses connections.

This guide includes the following sections:

• Event Descriptions describes the connection pool events that the driver can generate.

• Event Subscription Example provides sample code that shows how to subscribe to connection pool events.

• Example Event Documents provides samples of each connection pool event.

• Additional Information provides links to resources and API documentation for types and methods mentioned in this guide.

Event Descriptions

You can monitor the following connection pool events:

Event Monitoring Example

You can monitor connection pool events by assigning an EventHandler instance as the value of the cmap_event_handler client option. To construct an EventHandler, which processes all connection pool events, use the callback() or async_callback() method.

The following example connects to a MongoDB deployment, instructs the client to monitor connection pool events, and prints each event:

let mut client_options = ClientOptions::parse("<connection string>").await?;
client_options.cmap_event_handler = Some(EventHandler::callback(|ev| println!("{:?}", ev)));
let client = Client::with_options(client_options)?;
// ... perform actions with the client to generate events

Example Event Documents

The following sections show sample output for each type of connection pool monitoring event.

PoolCreatedEvent {
  address: ...,
  options: {...}
}

PoolReadyEvent {
  address: ...
}

PoolClearedEvent {
  address: ...,
  service_id: ...,
}

PoolClosedEvent {
  address: ...
}

ConnectionCreatedEvent {
  address: ...,
  connection_id: 1
}

ConnectionReadyEvent {
  address: ...,
  connection_id: 1
}

ConnectionClosedEvent {
  address: ...,
  connection_id: 1,
  reason: ...,
  /* private fields */
}

ConnectionCheckOutStartedEvent {
  address: ...,
}

ConnectionCheckOutFailedEvent {
  address: ...,
  reason: ...,
  /* private fields */
}

ConnectionCheckedOutEvent {
  address: ...,
  connection_id: 1
}

ConnectionCheckedInEvent {
  address: ...,
  connection_id: 1
}

Additional Information

To learn more about monitoring a MongoDB deployment, see the How to Monitor MongoDB article.

To learn more about connecting to MongoDB, see the Connection Guide.

To learn more about improving the performance of your application, see the guide on Performance Considerations.