Does findAndModify effectively lock the document to prevent update conflicts?

Question

What type of locking does findAndModify() offer? Is is a write lock only, or read/write? Does it prevent simultaneous updates on the same record?

Answer 1

MongoDB has a global (per-instance) write lock, which serializes all updates across all data in the server (though different servers in a sharded cluster will each have their own independent locks). This means that at any given instant in time, only one update is taking place on any document, and therefore only one update for any given document.

findAndModify doesn't do anything different in this regard than an ordinary update -- it just returns the document to you.