Mongo and Minimongo

Meteor ships two implementations of the Mongo API in one codebase. The server talks to MongoDB through an async driver. The client runs Minimongo, an in-memory synchronous Mongo emulator that holds the documents that subscriptions have shipped.

Decision flow

1. Where does this code run?
   • Server-only: use await Collection.*Async(...).
   • Client-only: use Collection.*(...) synchronously.
   • Isomorphic (import in shared code): use await Collection.*Async(...). On the client the work is local but still Promise-based; on the server it talks to Mongo.
2. Does the query select more than a page of documents? Add { limit, skip } and an index that matches the selector.
3. Are you reading from a publication on the client? Use find().fetch() (sync) without await. The data is already local.