Profiler for slow queries in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the MongoDB profiler?

The MongoDB profiler helps find slow queries and operations by recording detailed information about database activities, so you can improve performance.

beginner

How do you enable the MongoDB profiler to log slow queries only?

Use db.setProfilingLevel(1, { slowms: 100 }) to log queries slower than 100 milliseconds.

beginner

Where does MongoDB store the profiler data?

Profiler data is stored in the system.profile collection inside the current database.

beginner

What command shows the current profiling level in MongoDB?

Run db.getProfilingStatus() to see the current profiler level and slowms threshold.

intermediate

How can you find the slowest queries recorded by the profiler?

Query db.system.profile.find().sort({ millis: -1 }).limit(5) to get the top 5 slowest queries.

What profiling level logs all database operations in MongoDB?

A 2

B 1

C 3

D 0

Level 2 logs all operations, including slow and fast queries.

Which collection holds the profiler data in MongoDB?

A system.operations

B system.logs

C system.slowqueries

D system.profile

Profiler data is stored in the system.profile collection.

How do you set the profiler to log only queries slower than 200ms?

A db.setProfilingLevel(1, { slowms: 200 })

B db.setProfilingLevel(2, { slowms: 200 })

C db.setProfilingLevel(0, { slowms: 200 })

D db.setProfilingLevel(1)

Level 1 with slowms option logs only slow queries above 200ms.

Which command shows the current profiler status?

A db.profileStatus()

B db.showProfiling()

C db.getProfilingStatus()

D db.getProfile()

db.getProfilingStatus() returns the current profiling level and slowms.

What does the millis field in profiler data represent?

A Number of documents scanned

B Query execution time in milliseconds

C Number of indexes used

D Size of the result set

The millis field shows how long the query took to run in milliseconds.

Explain how to enable and use the MongoDB profiler to find slow queries.

Think about setting the profiler level and where to find the data.

Describe the difference between profiling levels 0, 1, and 2 in MongoDB.

Consider what each level records.