[SERVER-82079] Count clustered index scan as indexScan and not collectionScan in $lookup explain output Created: 11/Oct/23  Updated: 14/Nov/23

Status: Backlog
Project: Core Server
Component/s: None
Affects Version/s: None
Fix Version/s: None

Type: Bug Priority: Major - P3
Reporter: Tarun Gaur (Inactive) Assignee: Backlog - Query Execution
Resolution: Unresolved Votes: 1
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Assigned Teams:
Query Execution
Operating System: ALL
Participants:

 Description   

Based on this community post: https://www.mongodb.com/community/forums/t/clustered-collections-as-lookup-target/246893

The user is worried we are not using clustered index, because in explain output for $lookup they see a lot of collectionScans and no indexes used.

It happens because internally clustered index scan is a collection scan and not an index scan.

We should improve explain output by showing explicitly that clustered index is used.


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