[SERVER-79551] Support pathless $count over timeseries Created: 31/Jul/23  Updated: 27/Oct/23  Resolved: 30/Aug/23

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

Type: Task Priority: Major - P3
Reporter: Irina Yatsenko (Inactive) Assignee: Backlog - Query Integration
Resolution: Gone away Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Assigned Teams:
Query Integration
Participants:

 Description   

$count query is rewritten as $group+$project over $_internalUnpackBucket stage so it is an include bucket spec but it might have no fields listed if there is no filter prior to counting. Ideally, we should support lowering such queries to SBE but if producing the right count of "empty documents" from the container stages proves to be tricky we should ensure the perf doesn't regress (either because it's OK to lower the prefix of the pipeline or because we block the lowering completely)



 Comments   
Comment by Irina Yatsenko (Inactive) [ 30/Aug/23 ]

yoonsoo.kim@mongodb.com Thanks for flagging this! Yes, the recent changes for PM-3324 have modified the plans, created for $count, and we don't need to worry about the correctness of this scenario anymore though SERVER-80323 looks like a similar concern (an include spec with no fields). I've also filed SERVER-80561 to follow up on perf for $count queries.

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