MonoDb creates connection every single operation on collection - mongodb

Question

I'm using mongodb-java-driver, and nothing else except that. I created singleten EJB with connection to Mongo.
#Singleton
public class MongoConnection {
private DB db = null;
private MongoClient mongoClient = null;
#PostConstruct
public void init() {
try {
mongoClient = new MongoClient("localhost", 27017);
db = mongoClient.getDB("mydb");
} catch (UnknownHostException e) {
e.printStackTrace();
}
}
public MongoConnection() {
}
public DB getDb() {
return db;
}
public DBCollection getCollectionInDatabase(String collection) {
DBCollection coll;
coll = db.getCollection(collection);
return coll;
}
}
I get this ejb in ApplicationScoped bean (JSF) (just to be sure, that I will have only ONE instance of DB connection).
#Named("appMongo")
#ApplicationScoped
public class MongoApplicationScope implements Serializable{
private static final long serialVersionUID = 1L;
#EJB MongoConnection mu;
public MongoConnection getMu() {
return mu;
}
public void setMu(MongoConnection mu) {
this.mu = mu;
}
}
Then in request scoped bean I get data from db
#Named("mongoBean")
#SessionScoped
public class MongoBean implements Serializable {
private static final long serialVersionUID = 1L;
#Inject MongoApplicationScope mongoAccess;
public void mongoDzialanie() {
DBCollection coll = mongoAccess.getMu().getDb().getCollection("oko"); //at this step everything is correct
System.out.println(coll.getCount()); //new connection is created text from mongoDB console -> connection accepted from 127.0.0.1:57700 #2 (2 connections now open)
}
Why even if I have the same "db" object instance I can't get data without creating new connection, why I can't share this connection as it should be due to pooling?
}

Answer 1

MongoDB drivers open new connections on the background each time you work with a collection. Drivers decide when to open a new one. I believe it depends on the driver's implementation.
You can control the max number of connections opened by setting poolSize value (default is 5 for Node.JS MongoDb driver http://mongodb.github.io/node-mongodb-native/2.2/api/MongoClient.html#connect) It could be different for Java or other languages. Check your documentation.
If you are going to have more than one db object, each object will have its own connection pool. In my case I have mainDb and logsDb. Each have pool of 10. Therefore, up to 20 concurrent connections will be opened.
Finally, if you are using node.js driver, make sure to pass Number as value and not string (i.e poolSize:10). This will save you hours/days of troubleshooting :)