错误信息如下：

(node) warning: possible EventEmitter memory leak detected. 11 listeners added. Use emitter.setMaxListeners() to increase limit.
Trace
    at addListener (events.js:160:15)
    at Server.connect (e:\work\blog\node_modules\mongodb\lib\server.js:291:17)
    at Db.open (e:\work\blog\node_modules\mongodb\lib\db.js:190:19)
    at Function.Post.getAll (e:\work\blog\modles\post.js:57:13)
    at e:\work\blog\routes\index.js:13:14
    at Layer.handle [as handle_request] (e:\work\blog\node_modules\express\lib\router\layer.js:82:5)
    at next (e:\work\blog\node_modules\express\lib\router\route.js:110:13)
    at Route.dispatch (e:\work\blog\node_modules\express\lib\router\route.js:91:3)
    at Layer.handle [as handle_request] (e:\work\blog\node_modules\express\lib\router\layer.js:82:5)
    at e:\work\blog\node_modules\express\lib\router\index.js:267:22
(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 connectHandler (e:\work\blog\node_modules\mongodb\lib\server.js:265:19)
    at g (events.js:180:16)
    at emit (events.js:95:17)
    at e:\work\blog\node_modules\mongodb\node_modules\mongodb-core\lib\topologies\server.js:373:23
    at e:\work\blog\node_modules\mongodb\node_modules\mongodb-core\lib\topologies\server.js:770:13
    at Callbacks.emit (e:\work\blog\node_modules\mongodb\node_modules\mongodb-core\lib\topologies\server.js:84:3)
    at null.messageHandler (e:\work\blog\node_modules\mongodb\node_modules\mongodb-core\lib\topologies\server.js:218:23)
    at Socket.<anonymous> (e:\work\blog\node_modules\mongodb\node_modules\mongodb-core\lib\connection\connection.js:259:22)

这是什么问题，怎么解决？