Loading...

XML

Word

Printable

JSON

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

Assigned Teams:

Query Optimization
Sprint:
Query 2019-07-29
Case:
Confidence Status:
None

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

A very common use of an aggregation is to count elements by group:

db.items.aggregate([ {$group: {_id: "$category", count: {$sum: 1}}}])

If there is an index over category, this pipeline could be covered and no document retrieval is necessary.

Since this is a quite common pattern, you may take it into account and make use of indexes.

is related to

SERVER-57518 16% performance loss switching from Count to CountDocuments

Backlog

SERVER-20066 Query planner should consider index scans on empty query predicates

Closed

related to

SERVER-69257 COUNT_SCAN plan not selected when unfiltered $group + $sum on _id performed

Backlog

SERVER-4507 aggregation: optimize $group to take advantage of sorted sequences

Backlog

Assignee:: Unassigned

Reporter:: Nicolas Dascanio

Participants:: Asya Kamsky, David Storch, Kelsey Schubert, Kyle Suarez, Nicolas Dascanio

Votes:: 13 Vote for this issue

Watchers:: 29 Start watching this issue

Created:: Jun 04 2017 10:00:11 PM UTC

Updated:: Mar 06 2025 03:51:29 PM UTC