MongoDB configuration in a java web app

Question

I'm looking for some advice on the proper way to set up mongoDB for my web application that runs with java. From the mongoDB tutorial, i understand that I should have only one instance of the Mongo class.

The Mongo class is designed to be thread safe and shared among threads. Typically you create only 1 instance for a given DB cluster and use it across your app.

So I've got a singleton provider for this (I'm using guice for injection)

@Singleton
public class MongoProvider implements Provider<Mongo> {
    private Mongo mongo;

    public Mongo get() {
        if (mongo == null)
            mongo = new Mongo("localhost", 27017);
        return mongo;
    }
}

And whenever I have to work with mongo in my webapp i inject the provider and get the same instance of mongo.

public class MyService {
    private Provider<Mongo> mongoProvider;

    @Inject
    private MyService(Provider<Mongo> mongoProvider) {
        this.mongoProvider = mongoProvider;
    }

    public void execute() {
        DB db = mongoProvider.get().getDB("mydatabase");
        DBCollection coll = db.getCollection("mycollection");

        // Do stuff in collection
        ...
    }
}

What I find weird is that everytime i access my database, i get logs like this from mongo :

[initandlisten] connection accepted from 192.168.1.33:54297 #15

[initandlisten] connection accepted from 192.168.1.33:54299 #16

So far, I haven't had any problems but I'm wondering if it's good practice and if I won't run into any problems when the number of connections accepted gets too high.

Should I also have only one instance of the DB object for my entire app ?
Do I have to configure MongoDB differently to automatically close the connections after some time ? Or do I have to close connections manually ? I've read something about using the close() method on Mongo but I'm not sure when or if to call it.

Thank you for you advice.

score 1 · Accepted Answer · answered Jun 01 '12 at 15:02

This is good practice. Each instance of Mongo manages a connection pool, so you will see multiple connections in the mongod logs, one for each connection in the pool. The default pool size is 10, but that can be configures using the connectionsPerHost field in MongoOptions.

Mongo instances also maintain a cache of DB instances, so you don't have to worry about maintaining those as singletons yourself.

You do not have to configure Mongo to automatically close connections. You can call Mongo#close at the appropriate time to close all the sockets in the connection pool.

AdrianX · Answer 2 · 2013-04-29T15:33:02.670

Founded something like this om MondoDB site:

"The Java MongoDB driver is thread safe. If you are using in a web serving environment, for example, you should create a single MongoClient instance, and you can use it in every request. The MongoClient object maintains an internal pool of connections to the database (default pool size of 10). For every request to the DB (find, insert, etc) the Java thread will obtain a connection from the pool, execute the operation, and release the connection. This means the connection (socket) used may be different each time."

And from FAQ from MongoSite which I think completely anwsers on you question.

http://docs.mongodb.org/manual/faq/developers/#why-does-mongodb-log-so-many-connection-accepted-events

MongoDB configuration in a java web app

2 Answers2