switching the default database on an open connection will quickly start
emitting "too many listeners" node warnings. There needs to be a way of
removing the listeners that are no longer needed.

The context is a server where each request first selects the db to
access the correct collections. There are many dbs and many
concurrent requests.

to reproduce:

mongoClient = require('mongodb').MongoClient;

mongoClient.connect("mongodb://localhost", function(err, db) {
  for (i=0; i<10; i++) {
    db.db("test")
  }
  db.close();
});

outputs 7 warnings from a set of mostly adjacent lines:

(node) warning: possible EventEmitter memory leak detected. 11 listeners added. Use emitter.setMaxListeners() to increase limit.
Trace
at addListener (events.js:160:15)
at once (events.js:185:8)
at new Db (/home/andras/node_modules/mongodb-2.0.28/lib/db.js:163:12)
at Db.db (/home/andras/node_modules/mongodb-2.0.28/lib/db.js:783:12)
at /home/andras/mongo-listener-test.js:5:8
at /home/andras/node_modules/mongodb-2.0.28/lib/mongo_client.js:403:11
at process._tickCallback (node.js:419:13)
(node) warning: possible EventEmitter memory leak detected. 11 listeners added. Use emitter.setMaxListeners() to increase limit.
Trace
at addListener (events.js:160:15)
at once (events.js:185:8)
at new Db (/home/andras/node_modules/mongodb-2.0.28/lib/db.js:164:12)
at Db.db (/home/andras/node_modules/mongodb-2.0.28/lib/db.js:783:12)
at /home/andras/mongo-listener-test.js:5:8
at /home/andras/node_modules/mongodb-2.0.28/lib/mongo_client.js:403:11
at process._tickCallback (node.js:419:13)
(node) warning: possible EventEmitter memory leak detected. 11 listeners added. Use emitter.setMaxListeners() to increase limit.
Trace
at addListener (events.js:160:15)
at once (events.js:185:8)
at new Db (/home/andras/node_modules/mongodb-2.0.28/lib/db.js:165:12)
at Db.db (/home/andras/node_modules/mongodb-2.0.28/lib/db.js:783:12)
at /home/andras/mongo-listener-test.js:5:8
at /home/andras/node_modules/mongodb-2.0.28/lib/mongo_client.js:403:11
at process._tickCallback (node.js:419:13)
(node) warning: possible EventEmitter memory leak detected. 11 listeners added. Use emitter.setMaxListeners() to increase limit.
Trace
at addListener (events.js:160:15)
at once (events.js:185:8)
at new Db (/home/andras/node_modules/mongodb-2.0.28/lib/db.js:166:12)
at Db.db (/home/andras/node_modules/mongodb-2.0.28/lib/db.js:783:12)
at /home/andras/mongo-listener-test.js:5:8
at /home/andras/node_modules/mongodb-2.0.28/lib/mongo_client.js:403:11
at process._tickCallback (node.js:419:13)
(node) warning: possible EventEmitter memory leak detected. 11 listeners added. Use emitter.setMaxListeners() to increase limit.
Trace
at addListener (events.js:160:15)
at once (events.js:185:8)
at new Db (/home/andras/node_modules/mongodb-2.0.28/lib/db.js:168:12)
at Db.db (/home/andras/node_modules/mongodb-2.0.28/lib/db.js:783:12)
at /home/andras/mongo-listener-test.js:5:8
at /home/andras/node_modules/mongodb-2.0.28/lib/mongo_client.js:403:11
at process._tickCallback (node.js:419:13)
(node) warning: possible EventEmitter memory leak detected. 11 listeners added. Use emitter.setMaxListeners() to increase limit.
Trace
at addListener (events.js:160:15)
at once (events.js:185:8)
at new Db (/home/andras/node_modules/mongodb-2.0.28/lib/db.js:169:12)
at Db.db (/home/andras/node_modules/mongodb-2.0.28/lib/db.js:783:12)
at /home/andras/mongo-listener-test.js:5:8
at /home/andras/node_modules/mongodb-2.0.28/lib/mongo_client.js:403:11
at process._tickCallback (node.js:419:13)
(node) warning: possible EventEmitter memory leak detected. 11 listeners added. Use emitter.setMaxListeners() to increase limit.
Trace
at addListener (events.js:160:15)
at new Db (/home/andras/node_modules/mongodb-2.0.28/lib/db.js:170:12)
at Db.db (/home/andras/node_modules/mongodb-2.0.28/lib/db.js:783:12)
at /home/andras/mongo-listener-test.js:5:8
at /home/andras/node_modules/mongodb-2.0.28/lib/mongo_client.js:403:11
at process._tickCallback (node.js:419:13)