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MongoDB Pub/Sub With Capped Collections

Rick Copeland designs a MongoDB Pub/Sub system based on:

  • MongoDB’s capped collections,
  • tailable data-awaiting cursors,
  • sequences (using find_and_modify()),
  • a “poorly documented option” of capped collections: oplog_replay1.

If you’ve been following this blog for any length of time, you know that my NoSQL database of choice is MongoDB. One thing that MongoDB isn’t known for, however, is building a publish / subscribe system. Redis, on the other hand, is known for having a high-bandwith, low-latency pub/sub protocol. One thing I’ve always wondered is whether I can build a similar system atop MongoDB’s capped collections, and if so, what the performance would be. Read on to find out how it turned out…

The solution is definitely ingenious and it could probably work for systems with not so many requirements for their pub/sub. It’s definitely a good excercise in combining some interesting features of MongoDB (I like the capped collections and the tailable data-awaiting cursors).

✚ I’m wondering if the behavior of the tailable data-awaiting cursors is the one of the non-blocking polls.

  1. I don’t really understand how this works. 

Original title and link: MongoDB Pub/Sub With Capped Collections (NoSQL database©myNoSQL)