Atlas: fix bad query targeting (scanned vs returned ratio)

TL;DR: The Query Targeting alert means queries scan orders of magnitude more documents than they return. Trace it in the Real-Time Performance Panel and index the filter. Query targeting Symptom: the Query Targeting alert fires, or the Real-Time Performance Panel shows a high scanned-to-returned ratio. Sort by scanned.

The error

the Query Targeting alert fires, or the Real-Time Performance Panel shows a high scanned-to-returned ratio. Sort by scanned.

The fix

TL;DR: The Query Targeting alert means queries scan orders of magnitude more documents than they return. Trace it in the Real-Time Performance Panel and index the filter. Query targeting Symptom: the Query Targeting alert fires, or the Real-Time Performance Panel shows a high scanned-to-returned ratio. Sort by scanned.

The error

the Query Targeting alert fires, or the Real-Time Performance Panel shows a high scanned-to-returned ratio.

The fix

Query targeting

Symptom: the Query Targeting alert fires, or the Real-Time Performance Panel shows a high scanned-to-returned ratio.

Diagnose

Open the Real-Time Performance Panel during the slow period. It shows current operations with the documents-scanned vs documents-returned ratio per operation. Sort by scanned. The offenders are usually a $match on an unindexed field or a sort with no supporting index.

Confirm

explain("executionStats") on the offending shape. Confirm COLLSCAN or an in-memory SORT, and note the exact filter and sort fields.

Fix

Create a compound index covering the equality filters first, then the sort fields, then range filters (the ESR rule: equality, sort, range). One good compound index beats three single-field indexes.

Verify

Re-run the workload: the scanned-to-returned ratio in the RTPP drops toward 1:1, and the Query Targeting alert clears. If the alert persists, another shape is still scanning; repeat.

When to use this

• You are seeing this exact error message; match the block above, not just part of it.
• The failing call matches the scenario in the title: Atlas.
• You want the fastest verified fix before digging through logs.

When not to use this

• Your error text differs from the block above; close cousins often have different causes.
• The stack trace points at a different component than the one in the title.
• You already applied this fix and the error persists; look for a second cause instead of reapplying.

Compatibility

• Not pinned to a specific version; follows current Atlas behavior.

Real-Time Performance Panel scanned-vs-returned ratio and the Query Targeting alert per https://www.mongodb.com/docs/atlas/performance-advisor/ and https://www.mongodb.com/docs/atlas/alerts/, verified 2026-09-26.