[SERVER-59911] Investigate parallel execution for $lookup with a foreign sharded view Created: 13/Sep/21  Updated: 06/Dec/22

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

Type: Improvement Priority: Major - P3
Reporter: Hana Pearlman Assignee: Backlog - Query Optimization
Resolution: Unresolved Votes: 0
Labels: read-only-views
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Assigned Teams:
Query Optimization
Participants:

 Description   

After SERVER-59501, mongos allows a top-level $lookup stage to be executed in parallel across shards when it thinks the foreign namespace is sharded. However, it seems mongos does not have the necessary information to determine whether or not a foreign view is sharded. In that case, the namespace is treated like an unsharded collection, and the $lookup isn't parallelized.

This ticket is to investigate if it is possible for mongos to determine that the namespace is a sharded view and to parallelize the top-level $lookup execution in that case. 


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