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  1. Node.js Driver
  2. NODE-1270

Multiple databases causing EventEmitter warnings

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    • Type: Icon: Bug Bug
    • Resolution: Fixed
    • Priority: Icon: Minor - P4 Minor - P4
    • None
    • Affects Version/s: 3.0.0, 3.0.1
    • Component/s: None
    • Labels:
    • Environment:
      node v8.9.3

      Using more than 9 databases with one client (with a registered listener) causes MaxListenersExceededWarning: Possible EventEmitter memory leak detected warnings.

      The following snippet demonstrates the problem:

      const { MongoClient } = require('mongodb');

function connect(url) {
  return MongoClient.connect(url).then((client) => {
    client.on('authenticated', () => { console.log('authenticated:', url); });
    client.on('close', () => { console.log('close:', url); });
    client.on('error', () => { console.log('error:', url); });
    client.on('fullsetup', () => { console.log('fullsetup:', url); });
    client.on('parseError', () => { console.log('parseError:', url); });
    client.on('reconnect', () => { console.log('reconnect:', url); });
    client.on('reconnectFailed', () => { console.log('reconnectFailed:', url); });
    client.on('timeout', () => { console.log('timeout:', url); });
    return client;
  });
}

function useDb(client, dbName) {
  return client.then((c) => c.db(dbName));
}

const client = connect('mongodb://localhost');

const dbNames = ['foo1', 'foo2', 'foo3', 'foo4', 'foo5', 'foo6', 'foo7', 'foo8', 'foo9', 'foo10'];

dbNames.forEach((dbName) => {
  useDb(client, dbName);
});

      Output:

      (node:23675) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 error listeners added. Use emitter.setMaxListeners() to increase limit
(node:23675) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 timeout listeners added. Use emitter.setMaxListeners() to increase limit
(node:23675) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 close listeners added. Use emitter.setMaxListeners() to increase limit
(node:23675) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 parseError listeners added. Use emitter.setMaxListeners() to increase limit
(node:23675) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 open listeners added. Use emitter.setMaxListeners() to increase limit
(node:23675) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 fullsetup listeners added. Use emitter.setMaxListeners() to increase limit
(node:23675) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 all listeners added. Use emitter.setMaxListeners() to increase limit
(node:23675) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 reconnect listeners added. Use emitter.setMaxListeners() to increase limit

            Assignee:
            jessica.lord Jessica Lord
            Reporter:
            tjokimie Tuomo Jokimies
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              Created:
              Updated:
              Resolved: