The $lookup’s document states ’ Performs a left outer join to an unsharded collection in the same database to filter in documents from the “joined” collection for processing. ’
What does unsharded collection mean?
How will I know whether a collection I want to join with sharded or unsharded?
Why a sharded collection cannot be looked up?
Thank you
@JoSat_61332,
Unsharded Collection means the collection which is not shared across the cluster I mean with in other databases.
So in lookup stage you have to use only unsharded collections.
In brief sharded means a collection is shared across different databases (for example using indexes and partitions) if it has too much of data to load. This comes to overcome performance issues.
To get full idea on this topic reach out to this link:
https://docs.mongodb.com/manual/sharding/
Thank you very much.
A slight clarification. A sharded collection is one database where the data is shared across different clusters, not multiple databases. I’m pretty sure that’s what you meant here, but just to be clear…