Configure mongo for one shot full db read

I have a kubernetes cluster on bare metal with 3 machines having 8Gb of ram each. All my apps and a mongodb 4.0.9 replicaset runs on it. There is an import program that: 1. Download a 8Gb mongo dump from external source and restore it in fresly created database A. There is one collection whitout indexes. 2. Fully browse the restored collection with one find({}) and 1M next(). 3. Emit amqp messages for each doc, then messages are stored in mongo database B, C, D. 4. Drop the database A. Part 2 use a lot of ram. How should I configure mongo database A (and let database B normal) to reduce at max the footprint of the import operation? (Because more important tasks are running in the cluster) For example, can I configure mongo to not create cache for the temporary collection?