Performance Optimization with Indexes

1. Introduction

Tutorial Goal

This tutorial aims to teach you how to optimize your MongoDB database performance by effectively using indexes.

What You Will Learn

By the end of this tutorial, you should be able to:
- Understand the importance of indexing in MongoDB
- Create, drop, and manage indexes in MongoDB
- Apply best practices for indexing in MongoDB

Prerequisites

You should have a basic understanding of MongoDB and how to use it. Basic knowledge of JavaScript (or another language MongoDB supports) is also recommended.

2. Step-by-Step Guide

MongoDB Indexing

Indexes are essential to efficient data retrieval. Without them, MongoDB must perform a collection scan, i.e., scan every document in a collection, to select those that match the query statement. With an index, MongoDB can limit the search to the index entries, thereby improving performance.

To create an index, you use the db.collection.createIndex() method:

db.collection.createIndex( { field1: 1, field2: -1 } )

The 1 and -1 values are sort orders, representing ascending and descending, respectively.

Indexing Best Practices

1. Index Selectivity: An index is more selective when it filters out more documents in the collection. Higher selectivity indexes lead to fewer documents scanned, increasing query performance.
2. Covered Queries: These are queries in which the fields in the query are part of an index and the fields returned in the results are in the same index.
3. Indexing Order: In compound indexes, order matters. That is, the order of fields in the index should match the order in your queries.
4. Avoid Indexing Large Field Values: Large indexes can lead to increased I/O and decreased performance.

3. Code Examples

Create an Index

// Create an ascending index on the "username" field
db.users.createIndex( { "username": 1 } )

Create a Compound Index

// Create a compound index: "username" ascending and "date" descending
db.users.createIndex( { "username": 1, "date": -1 } )

Delete an Index

// Delete the index on the "username" field
db.users.dropIndex( { "username": 1 } )

4. Summary

In this tutorial, you learned about the importance of MongoDB indexing for query performance. You learned how to create, manage, and delete indexes, and you discovered some best practices for MongoDB indexing.

5. Practice Exercises

1. Exercise 1: Create a compound index on the orders collection for the fields item (ascending) and date (descending).
2. Exercise 2: Delete the index you created in Exercise 1.
3. Exercise 3: Create a covered query using an index.

Solutions

1. Solution 1: db.orders.createIndex( { "item": 1, "date": -1 } )
2. Solution 2: db.orders.dropIndex( { "item": 1, "date": -1 } )
3. Solution 3: First, create an index: db.orders.createIndex( { "item": 1, "date": 1 } ). Then, make a covered query: db.orders.find( { "item": "book", "date": { $gte: new Date('2022-01-01') } }, { _id: 0, item: 1, date: 1 } )

Continue practicing by creating and managing indexes on different fields and creating covered queries. Happy learning!