[SERVER-40905] Explain should indicate when aggregation pipeline optimizations occur Created: 30/Apr/19  Updated: 06/Dec/22

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

Type: Improvement Priority: Major - P3
Reporter: Chris Harris Assignee: Backlog - Query Optimization
Resolution: Unresolved Votes: 1
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
Related
related to SERVER-35069 Explain should include command being ... Closed
Assigned Teams:
Query Optimization
Participants:
Case:

 Description   

The optimizer can perform a variety of optimizations on an aggregation pipeline.  These include reordering of stages as well as coalescence.  Such modifications allow the database to improve the performance of the pipeline.  

To determine if any of these optimizations have happened, a user must be aware of their existence and then compare the stages output from explain with the original pipeline that was submitted.  Explain could help facilitate this process more directly by indicating specific optimizations that were performed.  This could be done via simple boolean flags or could be more complex and list out the transformations individually.



 Comments   
Comment by Asya Kamsky [ 02/May/19 ]

I think SERVER-35069 is related since one of its motivators is to be able to see that executed pipeline differs from input pipeline.

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