Profiler for slow queries in MongoDB - Mini Project: Build & Apply

Profiler for Slow Queries in MongoDB

📖 Scenario: You are a database administrator for a small online store. You want to find out which queries are running slowly in your MongoDB database so you can improve performance.

🎯 Goal: Build a simple MongoDB profiler setup that records slow queries and then query the profiler data to find those slow queries.

📋 What You'll Learn

Enable the MongoDB profiler to log slow queries

Set a threshold for what counts as a slow query

Query the profiler collection to find slow queries

Limit the output to the slowest queries

💡 Why This Matters

🌍 Real World

Database administrators use profiling to identify slow queries that affect application performance and user experience.

💼 Career

Knowing how to use the MongoDB profiler is important for roles like DBA, backend developer, and performance engineer.

1

Enable the MongoDB profiler

Enable the MongoDB profiler on the current database with level 1 to log slow queries.

MongoDB

// Enable the profiler with level 1
// Your code here

Need a hint?

Use db.setProfilingLevel(1) to enable profiling of slow queries.

2

Set the slow query threshold

Set the slow query threshold to 100 milliseconds using slowms option in the profiler configuration.

MongoDB

db.setProfilingLevel(1)
// Set slowms to 100 milliseconds
// Your code here

Need a hint?

Use db.setProfilingLevel(1, { slowms: 100 }) to set the threshold.

3

Query the profiler for slow queries

Write a query on the system.profile collection to find all queries where millis is greater than 100.

MongoDB

db.setProfilingLevel(1, { slowms: 100 })
// Query system.profile for slow queries
// Your code here

Need a hint?

Use db.system.profile.find({ millis: { $gt: 100 } }) to find slow queries.

4

Sort and limit the slow queries output

Modify the query to sort the slow queries by millis in descending order and limit the output to 5 documents.

MongoDB

db.setProfilingLevel(1, { slowms: 100 })
// Sort by millis descending and limit to 5
// Your code here

Need a hint?

Use .sort({ millis: -1 }) and .limit(5) on the query.