Today I learned:
Using $lookup (mongo 4.4) with pipeline, $match only uses index if we are using $eq
Other than that it wont use index and that will causes performance issue.
References:
- https://groups.google.com/g/mongodb-user/c/lvRsC-RRHpc/m/EFTTJfKGCQAJ
- https://www.mongodb.com/docs/v4.4/reference/operator/aggregation/lookup/
Using $lookup (mongo 4.4) with pipeline, $match only uses index if we are using $eq
Other than that it wont use index and that will causes performance issue.
References:
- https://groups.google.com/g/mongodb-user/c/lvRsC-RRHpc/m/EFTTJfKGCQAJ
- https://www.mongodb.com/docs/v4.4/reference/operator/aggregation/lookup/
The $expr operator only uses indexes on the from collection for equality matches. Non-equality match queries, such as range queries, cannot use indexes on the from collection.