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- Reference
- Management
- Connection Pool Monitoring
Connection Pool Monitoring
The Node.js driver 3.5.0 or higher features Connection Pool Monitoring events, allowing an application or
tool to monitor the internal workings of the driver’s connection pool.
NOTE: Connection pool monitoring is only available when the “Unified Topology” is enabled
Overview of CMAP events
| Event | Description |
|---|---|
| connectionPoolCreated | Emitted when a connection pool is created |
| connectionPoolClosed | Emitted when a connection pool is closed, prior to server instance destruction |
| connectionCreated | Emitted when a connection is created, but not necessarily when it is used for an operation |
| connectionReady | Emitted after a connection has successfully completed a handshake, and is ready to be used for operations |
| connectionClosed | Emitted when a connection is closed |
| connectionCheckOutStarted | Emitted when an operation attempts to acquire a connection for execution |
| connectionCheckOutFailed | Emitted when an operation fails to acquire a connection for execution |
| connectionCheckedOut | Emitted when an operation successfully acquires a connection for execution |
| connectionCheckedIn | Emitted when a connection is returned to the pool after operation execution |
| connectionPoolCleared | Emitted when the connection pool’s generation count is increased |
Simple Code Example
The following example demonstrates connecting to a replica set and printing out all CMAP related events:
const MongoClient = require('mongodb').MongoClient;
const url = 'mongodb://localhost:31000,localhost:31001/?replicaSet=rs';
const client = new MongoClient(url);
client.on('connectionPoolCreated', event => console.dir(event));
client.on('connectionPoolClosed', event => console.dir(event));
client.on('connectionCreated', event => console.dir(event));
client.on('connectionReady', event => console.dir(event));
client.on('connectionClosed', event => console.dir(event));
client.on('connectionCheckOutStarted', event => console.dir(event));
client.on('connectionCheckOutFailed', event => console.dir(event));
client.on('connectionCheckedOut', event => console.dir(event));
client.on('connectionCheckedIn', event => console.dir(event));
client.on('connectionPoolCleared', event => console.dir(event));
client.connect((err, client) => {
if (err) throw err;
});
Example Events
connectionPoolCreated
ConnectionPoolCreatedEvent {
time: 2020年01月14日T13:46:15.536Z,
address: 'localhost:31003',
options: { ... }
}
connectionPoolClosed
ConnectionPoolClosedEvent {
time: 2020年01月14日T13:54:53.570Z,
address: '127.0.0.1:34849'
}
connectionCreated
ConnectionCreatedEvent {
time: 2020年01月14日T13:54:53.579Z,
address: '127.0.0.1:34849',
connectionId: 1
}
connectionReady
ConnectionReadyEvent {
time: 2020年01月14日T13:54:53.579Z,
address: '127.0.0.1:34849',
connectionId: 1
}
connectionClosed
ConnectionClosedEvent {
time: 2020年01月14日T13:54:53.564Z,
address: '127.0.0.1:34849',
connectionId: 2,
reason: ...
}
connectionCheckOutStarted
ConnectionCheckOutStartedEvent {
time: 2020年01月14日T13:49:59.271Z,
address: 'localhost:31000'
}
connectionCheckOutFailed
ConnectionCheckOutFailedEvent {
time: 2020年01月14日T13:49:59.271Z,
address: 'localhost:31000'
reason: ...
}
connectionCheckedOut
ConnectionCheckedOutEvent {
time: 2020年01月14日T13:48:42.541Z,
address: 'localhost:31000',
connectionId: 1
}
connectionCheckedIn
ConnectionCheckedInEvent {
time: 2020年01月14日T13:48:42.543Z,
address: 'localhost:31000',
connectionId: 1
}
connectionPoolCleared
ConnectionPoolClearedEvent {
time: 2020年01月14日T13:58:11.437Z,
address: '127.0.0.1:45005'
}
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