Index usage verification in MongoDB - Mini Project: Build & Apply

Index Usage Verification in MongoDB

📖 Scenario: You are managing a MongoDB database for a small online bookstore. To make searching for books faster, you want to use indexes on certain fields.

🎯 Goal: Learn how to create an index on a MongoDB collection and verify that the index is being used by queries.

📋 What You'll Learn

Create a MongoDB collection called books with sample book documents

Create an index on the author field

Run a query filtering by author and verify index usage with explain()

Check the query plan to confirm the index is used

💡 Why This Matters

🌍 Real World

Indexes in databases help speed up searches, just like an index in a book helps you find pages quickly.

💼 Career

Database administrators and backend developers use index creation and verification to optimize application performance.

1

Create the books collection with sample data

Insert three documents into the books collection with these exact fields and values: { title: "The Hobbit", author: "J.R.R. Tolkien", year: 1937 }, { title: "1984", author: "George Orwell", year: 1949 }, and { title: "To Kill a Mockingbird", author: "Harper Lee", year: 1960 }.

MongoDB

// Insert the three book documents into the books collection

Need a hint?

Use db.books.insertMany() with an array of objects for the books.

2

Create an index on the author field

Create an ascending index on the author field in the books collection using db.books.createIndex().

MongoDB

db.books.insertMany([
  { title: "The Hobbit", author: "J.R.R. Tolkien", year: 1937 },
  { title: "1984", author: "George Orwell", year: 1949 },
  { title: "To Kill a Mockingbird", author: "Harper Lee", year: 1960 }
])
// Create an ascending index on the author field below

Need a hint?

Use db.books.createIndex({ author: 1 }) to create an ascending index on the author field.

3

Run a query filtering by author and use explain()

Write a query to find all books where author is exactly "George Orwell" using db.books.find(). Chain .explain() to this query to get the query plan.

MongoDB

db.books.insertMany([
  { title: "The Hobbit", author: "J.R.R. Tolkien", year: 1937 },
  { title: "1984", author: "George Orwell", year: 1949 },
  { title: "To Kill a Mockingbird", author: "Harper Lee", year: 1960 }
])
db.books.createIndex({ author: 1 })
// Query books by author "George Orwell" and add explain() below

Need a hint?

Use db.books.find({ author: "George Orwell" }).explain() to see the query plan.

4

Verify the index is used in the query plan

Check the query plan output from explain() and add a comment line that includes the phrase "IXSCAN" to indicate the index scan is used.

MongoDB

db.books.insertMany([
  { title: "The Hobbit", author: "J.R.R. Tolkien", year: 1937 },
  { title: "1984", author: "George Orwell", year: 1949 },
  { title: "To Kill a Mockingbird", author: "Harper Lee", year: 1960 }
])
db.books.createIndex({ author: 1 })
db.books.find({ author: "George Orwell" }).explain()
// Add a comment confirming the index scan is used

Need a hint?

Look for IXSCAN in the explain output and add a comment like // The query plan shows an IXSCAN.