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Type: Improvement
Resolution: Unresolved
Priority: Major - P3
Fix Version/s: None
Affects Version/s: None
Component/s: None
Labels:
- indexv3

Assigned Teams:

Query Optimization
Sprint:
QO 2021-10-04, QO 2021-10-18
Confidence Status:
None
Work Order:
3
CAR Domain/s:
None

Aha! Reference:
None
Tracking Level:
None
Risk Status:
None
Exec Notes:
None
Goal Name(s):
None
Goal Link:
None

MongoDB 4.2 introduced the ability to avoid full index scans for aggregation pipelines that include a specific type of $group stage - those that logically request distinct information which can be obtained by scanning a single document. This was initially implemented via ~~SERVER-9507~~.

As confirmed by this comment from a related enhancement in ~~SERVER-40090~~, this optimization currently only applies when the aggregation is grouping on a single field. We should consider expanding this optimization, or a similar one, to reduce index scanning when the _id specified for the $group is on multiple fields.

depends on

SERVER-21992 Inconsistent results when grouping by possibly missing values

Backlog

SERVER-14832 Distinct command result set may include or exclude null/undefined depending on presence of index

Needs Scheduling

SERVER-60977 Make $group _id behavior with null and missing more consistent

Closed

is duplicated by

SERVER-56294 Extend group to distinct optimization to compound keys

Closed

related to

SERVER-40090 DISTINCT_SCAN in agg is only used when certain format of _id is specified

Closed

Assignee:: [DO NOT USE] Backlog - Query Optimization
Reporter:: Chris Harris
Participants:: [DO NOT USE] Backlog - Query Optimization, Chris Harris, Katherine Wu, Ruslan Abdulkhalikov
Votes:: 3 Vote for this issue
Watchers:: 18 Start watching this issue

Created:: Jan 06 2021 10:30:25 PM UTC
Updated:: Jan 21 2023 02:54:33 AM UTC

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