TBD once we are further with scoping.

Summary

This project will allow $lookup or $graphLookup to execute when the 'from' namespace is sharded and add the ability to retrieve results from a different database.

Motivation

The $lookup stage is one of relatively few things that work on an unsharded collection but not on a sharded one. The fact that the 'from' collection cannot be sharded surprises many users and prevents its use in many sharded deployments. We think that supporting this stage is worth doing to remove the element of surprise, even if the performance is suboptimal. Removing the restriction will also aid in capturing more customer use cases.

Documentation

Scope document
Design document