Confusion about passing poolSize option while connecting to mongodb using mongodb-native(mongoClient)

[Vijay Kanshi]

I am little bit confused for passing the poolSize for replicaSet or sharded system

1. const opt = {poolSize:2}

2. const opt = {replSet: {poolSize:2}}.

Which way is better to pass poolSize for replicaSet or sharded system . 1 or 2nd ??

let MongoClient = require('mongodb’).MongoClient;

MongoClient.connect(url, opt , function(err ,  opened_db) {

})