Connection Monitoring

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Overview

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

Overview

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.

Subscribe to Events

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)

Event Descriptions

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.

Example Event Documents

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

ConnectionPoolCreated

*event.PoolEvent
{
    "type": "ConnectionPoolCreated",
    "address": "...",
    "connectionId": 0,
    "options": {
        "maxPoolSize": 100,
        "minPoolSize": 0,
        "maxIdleTimeMS": 0
    },
    "reason": "",
    "serviceId": null,
    "error": null
}

ConnectionPoolReady

*event.PoolEvent
{
    "type": "ConnectionPoolReady",
    "address": "...",
    "connectionId": 0,
    "options": null,
    "reason": "",
    "serviceId": null,
    "error": null
}

ConnectionPoolCleared

*event.PoolEvent
{
    "type": "ConnectionPoolCleared",
    "address": "...",
    "connectionId": 0,
    "options": null,
    "reason": "",
    "serviceId": null,
    "error": null
}

ConnectionPoolClosed

*event.PoolEvent
{
    "type": "ConnectionPoolClosed",
    "address": "...",
    "connectionId": 0,
    "options": null,
    "reason": "",
    "serviceId": null,
    "error": null
}

ConnectionCreated

*event.PoolEvent
{
    "type": "ConnectionCreated",
    "address": "...",
    "connectionId": 1,
    "options": null,
    "reason": "",
    "serviceId": null,
    "error": null
}

ConnectionReady

*event.PoolEvent
{
    "type": "ConnectionReady",
    "address": "...",
    "connectionId": 1,
    "options": null,
    "reason": "",
    "serviceId": null,
    "error": null
}

ConnectionClosed

*event.PoolEvent
{
    "type": "ConnectionClosed",
    "address": "...",
    "connectionId": 1,
    "options": null,
    "reason": "",
    "serviceId": null,
    "error": null
}

ConnectionCheckOutStarted

*event.PoolEvent
{
    "type": "ConnectionCheckOutStarted",
    "address": "...",
    "connectionId": 0,
    "options": null,
    "reason": "",
    "serviceId": null,
    "error": null
}

ConnectionCheckOutFailed

*event.PoolEvent
{
    "type": "ConnectionCheckOutFailed",
    "address": "...",
    "connectionId": 0,
    "options": null,
    "reason": "",
    "serviceId": null,
    "error": null
}

ConnectionCheckedOut

*event.PoolEvent
{
    "type": "ConnectionCheckedOut",
    "address": "...",
    "connectionId": 1,
    "options": null,
    "reason": "",
    "serviceId": null,
    "error": null
}

ConnectionCheckedIn

*event.PoolEvent
{
    "type": "ConnectionCheckedIn",
    "address": "...",
    "connectionId": 1,
    "options": null,
    "reason": "",
    "serviceId": null,
    "error": null
}

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.

API Documentation

To learn more about the methods and types mentioned in this guide, see the following API documentation:

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