The fact $inc (and other) is atomic is difficult to establish from the current documentation. $inc reference page does not mention it.

Searching for "atomic" only returns a page with a findAndModify example.

15:28 < ragezor> hello guys, i'm trying to implement a counter system in mongodb and i need advice about implementation
15:28 < ragezor> i have a collection counters and in there a lot of documents which represent one counter each
15:29 < Nodex> so far so good
15:29 < ragezor> counters have field number which then i increment each time an event occurs
15:29 < ragezor> my question is
15:29 < ragezor> if many different processes are incrementing the counter
15:30 < kali> if you're using $inc:1, it will work as you want it to work
15:30 < ragezor> can it happen that counter breaks, that is some increments are not registered?
15:31 < ragezor> so $inc is atomic operation?
15:31 < kali> yes
15:31 < ragezor> ok, cool