Atlas: diagnose slow queries with the profiler and Performance Advisor

Not specified by the original author.

TL;DR: Slow endpoint, unknown cause. The symptom to cause path runs through the Query Profiler and Performance Advisor to a suggested index, verified with explain. Confirm Run the query shape with explain("executionStats") in mongosh. Fix Create the suggested index.

The error

an endpoint or job is slow and you suspect the database.

The fix

Slow queries: profiler to index

Symptom: an endpoint or job is slow and you suspect the database.

Diagnose

1. Atlas UI: Performance Advisor. It lists slow query shapes grouped by pattern, with suggested indexes. This is only on M10+ clusters.
2. Cross-check with the Query Profiler (same area): it shows slow operations with key stats for the last few days, no extra cost.
3. Pick the worst shape by total time (frequency x avg duration), not the single slowest one-off.

Confirm

Run the query shape with explain("executionStats") in mongosh. Look at totalDocsExamined vs nReturned. A big ratio means the query scans far more than it returns: missing or wrong index.

Fix

Create the suggested index. The Performance Advisor can create it directly from the UI (one at a time), or run the createIndex in mongosh. Keep read/write ratio in mind: every index taxes writes.

Verify

Re-run explain: totalDocsExamined should collapse toward nReturned, and the stage should be IXSCAN. Then watch the Performance Advisor over the next day to confirm the shape dropped off the slow list.

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.

Performance Advisor slow-query monitoring and suggested-index workflow per https://www.mongodb.com/docs/atlas/performance-advisor/; Query Profiler coverage of recent slow operations per the same docs, verified 2026-09-26.