Why should you care?

You cannot fix what you cannot see. Connection storms and COLLSCAN spikes show up in metrics first.

See it live — copy this example

Open mongosh or MongoDB Compass, select database nosqlverse, then run the example. Change one field and run again.

db.serverStatus().connections
db.serverStatus().opcounters
db.currentOp({ active: true, secs_running: { $gte: 1 } })
db.setProfilingLevel(1, { slowms: 100 })
db.system.profile.find().sort({ ts: -1 }).limit(3)

Run Example »

Edit the code below and click Run to see the result in Toolliyo’s live editor.

What happened?

• connections and opcounters are quick health signals.
• currentOp lists long runners.
• The profiler records slow operations over 100ms into system.profile — use carefully in prod (overhead).

Practice next

1. Enable Atlas alerts for CPU, disk, and connections.
2. Run serverStatus snippets on a practice DB.
3. Find one slow query via profiler or Atlas Performance Advisor.
4. Watch replication lag metrics on a replica set.
5. Export a weekly slow-query report.

Remember

Monitor connections, lag, and slow ops. Alert on thresholds that matter. Use profiler/advisor to find bad queries.

PagerDuty on connection spikes

A buggy deploy opens too many pools; Atlas alert fires; team rolls back.

Outcome: Outage avoided because monitoring caught saturation early.