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Hello,

When using $expr, a query that should be covered by the index actually examine documents.

Not only that, it searches for the values twice, once during the index scan and a second time during the fetch stage.

Screenshot 2026-03-16 at 17.27.35.png
Mar 16 2026 04:35:33 PM UTC
152 kB
Milena Ivanova
Screenshot 2026-03-16 at 17.29.01.png
Mar 16 2026 04:35:39 PM UTC
154 kB
Milena Ivanova

is depended on by

SERVER-110794 If all dependencies of $expr are provided by an index, don't generate FETCH

is duplicated by

SERVER-83529 Generate covered projections with $expr

SERVER-96826 $expr with find() does not use an index

is related to

SERVER-41171 MongoDB $lookup using "$expr" is slow compared to simple $lookup

SERVER-69680 allow $expr with comparison bounded by value and $type to use a non-multikey index

SERVER-96826 $expr with find() does not use an index

SERVER-106505 $sequentialCache optimization can interfere with $match pushdown in a $lookup sub-pipeline

related to

SERVER-109904 don't FETCH when expr has tight bounds of same type

(2 is related to, 1 related to)

Assignee:: Milena Ivanova
Reporter:: Miguel Ángel Nieto
Participants:: Asya Kamsky, Craig Homa, Githook User, Ivan Fefer, Miguel Ángel Nieto, Milena Ivanova
Votes:: 5 Vote for this issue
Watchers:: 29 Start watching this issue