how to enable debug on node.js and mongoDB native driver?

Question

i use node.js and node-mongodb-native driver, with connection pooling. is there any way to enable debug for see what's happening, how many connections are active and when a connection is opened or closed?

i would like to see something like:

* connection xxx opened on host:port
* connection yyy opened on host:port
* connection xxx closed

Answer 1

1. To watch the commands been sent to MongoDB, set the driver logger's level to debug.
2. To react to connection pool events, just subscribe to them and log yourself.
3. You may need the topology monitoring to react to changes of topology, such as joins to a secondary or disconnections with a replica set.

const client = new MongoClient('mongodb://127.0.0.1:27017/', {
  useUnifiedTopology: true,
  loggerLevel: 'debug',
  // logger: (message, context) => console.dir(context),
})

// connection pool monitoring
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))

// topology monitoring
client.on('serverDescriptionChanged', event => console.dir(event))
client.on('serverHeartbeatStarted', event => console.dir(event))
client.on('serverHeartbeatSucceeded', event => console.dir(event))
client.on('serverHeartbeatFailed', event => console.dir(event))
client.on('serverOpening', event => console.dir(event))
client.on('serverClosed', event => console.dir(event))
client.on('topologyOpening', event => console.dir(event))
client.on('topologyClosed', event => console.dir(event))
client.on('topologyDescriptionChanged', event => console.dir(event))