Add a $lookUp operator to the aggregation pipeline to pull data from one collection into a pipeline executed on a different collection.
- Aggregation stage to do left outer join
- Works across any shard/collection boundary
- left-hand side sharded, right-hand side unsharded
- Enforced collocation of “related” chunks.
- More parallelization for agg
- Small collections that co-exist on all shards (aka, “enum” collections)