Least intensive way to detect when mongo collection has changed?

help
1

I need to know when a collection has been changed in any way (document added,updated or removed). I don’t need to know what exactly has changed, just that a change has happened.

I’ve tried using for example

Collection.find().observe({
added: function(document){
    console.log('doc added');
},
changed:function(new_document, old_document){
        console.log('doc changed');
},
removed:function(document){
        console.log('doc removed');
}
});

The issue with this is that a significant (6.25%) CPU spike occurs every 30 seconds or so for a second or 2 on a collection of 2000 documents which is not ideal. This is on a 6700K CPU.

Any easy/neat way to do this? At the moment I’ve implemented a non-elegant solution of calling a function every time the collection is changed but this results in me having to call the function in 40+ places all over the application.

Sure I could go through and redo all my code so that the collection is only changed at a singular point, but before I do that I’m wondering if there is a better way.

2

I presume you’re talking about the server?

Are you using oplog? Search this forum for “oplog” and “performance”/“CPU” and you might find some useful posts, including one of mine.

Rather then observing the collection, try collection-hooks so you can automatically define a function to be called after any insert/update/remove command.

2 Likes
3

@wildhart’s suggestion, collection-hooks, should work very well but only if you are certain that the collection is always updated from within Meteor.

If you have services that update it from outside, and/or for low overhead, just use this NPM package: https://www.npmjs.com/package/mongo-oplog

We use it in production for a use case similar to yours.

1 Like
4

Ok thank you I’ll take a look at hooks

5

You could also do the same thing that they do in the todo sample app, extend Mongo.Collection. Again, will only work if this the db isn’t being updated externally:

 import { Mongo } from 'meteor/mongo';

class TodosCollection extends Mongo.Collection {
  insert(doc, callback) {
    const result = super.insert(doc, callback);
    // log change
    return result;
  }

  update(selector, modifier) {
    const result = super.update(selector, modifier);
    // log change
    return result;
  }

  remove(selector) {
    const result = super.remove(selector);
    // log change
    return result;
  }
}