[SERVER-59501] Investigate returning to original execution strategy when lookup 'from' is unsharded Created: 23/Aug/21  Updated: 29/Oct/23  Resolved: 13/Sep/21

Status: Closed
Project: Core Server
Component/s: None
Affects Version/s: None
Fix Version/s: 5.1.0-rc0

Type: Task Priority: Major - P3
Reporter: Katherine Wu (Inactive) Assignee: Hana Pearlman
Resolution: Fixed Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Backwards Compatibility: Fully Compatible
Sprint: QO 2021-09-06, QO 2021-09-20
Participants:

 Description   

As part of sharded $lookup, if the origin collection is sharded we will allow the $lookup stage to be moved to the shards part of the splitPipeline. We believe that executing the $lookup in parallel will be beneficial in most cases, however there are times when this is the wrong execution strategy. To avoid regressing existing workloads where the 'from' collection is unsharded, investigate the feasibility of "backing out" of this execution strategy in the DistributedPlanLogic of the DocumentSourceLookUp. The check for whether the 'from' collection is unsharded must be concurrency safe.



 Comments   
Comment by Vivian Ge (Inactive) [ 06/Oct/21 ]

Updating the fixversion since branching activities occurred yesterday. This ticket will be in rc0 when it’s been triggered. For more active release information, please keep an eye on #server-release. Thank you!

Comment by Githook User [ 13/Sep/21 ]

Author:

{'name': 'Hana Pearlman', 'email': 'hana.pearlman@mongodb.com', 'username': 'HanaPearlman'}

Message: SERVER-59501: Do not parallelize $lookup when foreign is unsharded
Branch: master
https://github.com/mongodb/mongo/commit/b5a51ca79626488c3caf153cc2d7f2178017bb8b

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