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Connection Monitoring

On this page

  • Overview
  • Subscribe to Events
  • Event Descriptions
  • Example Event Documents
  • ConnectionPoolCreated
  • ConnectionPoolReady
  • ConnectionPoolCleared
  • ConnectionPoolClosed
  • ConnectionCreated
  • ConnectionReady
  • ConnectionClosed
  • ConnectionCheckOutStarted
  • ConnectionCheckOutFailed
  • ConnectionCheckedOut
  • ConnectionCheckedIn
  • Additional Information
  • API Documentation

This guide shows you how to use the Go 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 might use information about connection pool events in your application to optimize performance or understand the client lifecycle.

You can access details about connection pool events by subscribing to them in your application. The following example demonstrates how to subscribe to the PoolEvent event by instantiating a PoolMonitor and connecting to a deployment:

var eventArray []*event.PoolEvent
cxnMonitor := &event.PoolMonitor{
Started: func(e *event.PoolEvent) {
eventArray = append(eventArray, e)
},
}
clientOpts := options.Client().ApplyURI(uri).SetPoolMonitor(cxnMonitor)
client, err := mongo.Connect(context.TODO(), clientOpts)

The following table describes the types of pool events that the driver emits:

Pool Event Type
Description
ConnectionPoolCreated
Created when a connection pool is created.
ConnectionPoolReady
Created when a connection pool is ready.
ConnectionPoolCleared
Created when all the connections in the pool are closed.
ConnectionPoolClosed
Created when a connection pool is closed, before the destruction of the server instance.
ConnectionCreated
Created when a connection is created, but not necessarily when it is used for an operation.
ConnectionReady
Created after a connection completes a handshake and is ready to be used for operations.
ConnectionClosed
Created when a connection is closed.
ConnectionCheckOutStarted
Created when an operation attempts to acquire a connection for execution.
ConnectionCheckOutFailed
Created when an operation cannot acquire a connection for execution.
ConnectionCheckedOut
Created when an operation successfully acquires a connection for execution.
ConnectionCheckedIn
Created when a connection is checked back into the pool after an operation is executed.

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

*event.PoolEvent
{
"type": "ConnectionPoolCreated",
"address": "...",
"connectionId": 0,
"options": {
"maxPoolSize": 100,
"minPoolSize": 0,
"maxIdleTimeMS": 0
},
"reason": "",
"serviceId": null,
"error": null
}
*event.PoolEvent
{
"type": "ConnectionPoolReady",
"address": "...",
"connectionId": 0,
"options": null,
"reason": "",
"serviceId": null,
"error": null
}
*event.PoolEvent
{
"type": "ConnectionPoolCleared",
"address": "...",
"connectionId": 0,
"options": null,
"reason": "",
"serviceId": null,
"error": null
}
*event.PoolEvent
{
"type": "ConnectionPoolClosed",
"address": "...",
"connectionId": 0,
"options": null,
"reason": "",
"serviceId": null,
"error": null
}
*event.PoolEvent
{
"type": "ConnectionCreated",
"address": "...",
"connectionId": 1,
"options": null,
"reason": "",
"serviceId": null,
"error": null
}
*event.PoolEvent
{
"type": "ConnectionReady",
"address": "...",
"connectionId": 1,
"options": null,
"reason": "",
"serviceId": null,
"error": null
}
*event.PoolEvent
{
"type": "ConnectionClosed",
"address": "...",
"connectionId": 1,
"options": null,
"reason": "",
"serviceId": null,
"error": null
}
*event.PoolEvent
{
"type": "ConnectionCheckOutStarted",
"address": "...",
"connectionId": 0,
"options": null,
"reason": "",
"serviceId": null,
"error": null
}
*event.PoolEvent
{
"type": "ConnectionCheckOutFailed",
"address": "...",
"connectionId": 0,
"options": null,
"reason": "",
"serviceId": null,
"error": null
}
*event.PoolEvent
{
"type": "ConnectionCheckedOut",
"address": "...",
"connectionId": 1,
"options": null,
"reason": "",
"serviceId": null,
"error": null
}
*event.PoolEvent
{
"type": "ConnectionCheckedIn",
"address": "...",
"connectionId": 1,
"options": null,
"reason": "",
"serviceId": null,
"error": null
}

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 the methods and types mentioned in this guide, see the following API documentation:

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