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javascriptmongodbmeteor
Adrian Lopez
Adrian Lopez

Reputation: 2887

Multiple DB in meteor keeping reactivity

There's some way to use more than one MongoDB database in meteor keeping reactivity/Oplog working? I've been reading about it (Post1), (Post2) and still I don't see a straighforward way to achieve this. It's possible? What's the right way? Thank you.

Upvotes: 1

Views: 115

Answers (2)

Adrian Lopez
Adrian Lopez

Reputation: 2887

I'm going to write here what I've discovered until now, but I'm not going to mark the question as answered.

Concepts

What is reactivity?

Using reactivity, the data you show to your users will be updated in real time. You can enable or disable reactivity when you subscribe to a collection. Like this:

// enabled by default
Meteor.publish('top', function() {
  return Top.find({},{reactive: false});
});

What is oplog?

Oplog is the MongoDB log. When you tell meteor to use oplog, reactivity performance is much better, unless you have a really high volumne of insert operations. In this cases may be wise to keep it disabled. Oplog can optimize your reactive DB calls by ~x5 ~x20.If you are going to use oplog you should optimize your db calls. You can read more about it here.

What methods exists to connect DBS to meteor?

Default connection:

Reactivity? yes. Oplog? yes. DB Limit? One. Description: Meteor creates a default MongoDB database when you run 'meteor'. You can set a different database using enviromental variables, or just MONGO_URL=mongodb://localhost:27017/db_name meteor.

DDP:

Reactivity? yes. Oplog? yes. DB Limit? no. Description: You need a meteor project for every DB. That's about 600MB in memory for every DB. You can read about it here and here.

MongoInternal (SOLUTION: Thanks to carlevans719):

Reactivity? yes. Oplog? yes. DB Limit? no. Description: You can specify a DB in your subscriptions file like:

ar database = new MongoInternals.RemoteCollectionDriver('mongodb://user:password@localhost:27017/meteor', {oplogUrl: "mongodb://localhost:27017/local"});
var numberOfDocs = database.open('boxes').find().count();

Last Words:

MongoInternal If you are not going to use the default db, you have to tell meteor to do not create it. To achieve this you must always run meteor as MONGO_URL=mongodb://localhost:27017 meteor

Upvotes: 0

carlevans719
carlevans719

Reputation: 106

As you say; Default Connection isn't really an option as you can only have one DB and DDP is a bit superfluous when you only need a DB and none of the Meteor stuff. I'd think, therefore, your best approach would be to use the MongoInternals option.

The only thing missing from that option is reactivity; a method of enabling oplog tailing for these additional DB connections is mentioned in this answer. It essentially seems to be a case of passing the oplogUrl when creating the RemoteCollectionDriver, here's the example given in their answer:

var driver = new MongoInternals.RemoteCollectionDriver(
    "mongodb://localhost:27017/db", 
    {
      oplogUrl: "mongodb://localhost:27017/local"
    });
var collection = new Mongo.Collection("Coll", {_driver: driver});

Upvotes: 1

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