How to easily find slow queries at MongoDB

Enable profiling

First, you have to enable profiling.

> db.setProfilingLevel(1)

Now let it run for a while. It collects the slow queries ( > 100ms) into a capped collections, so queries go in and if it’s full, old queries go out, so don’t be surprised that it’s a moving target.

Find the most recent slow query

> db.system.profile.find().sort({$natural: -1}).limit(1)

Find the single slowest query in the capped system.profile collection right now

> db.system.profile.find().sort({millis: -1}).limit(1)

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