[hiccuphippo]

Meteor.js used the MongoDB's oplog, which is used to replicate changes to other nodes, to provide real time update to it's clients.

You can query the oplog yourself easily [0]. I also remember someone doing a version for MySql using the same approach.

[0] http://www.briancarpio.com/2012/04/21/mongodb-the-oplog-expl...

[goliatone]

Mongo has now change streams[1] which use the aggregation framework so you can filter for specific updates or do transformations. You need v3.6, to have a replica set/cluster and run it with a flag to enable the behavior tho.

[1] https://docs.mongodb.com/manual/changeStreams/