Introduction to Indexes

Introduction

Indexes are MongoDB's most powerful performance tool. They turn full collection scans into targeted lookups. The cost: indexes consume RAM and slow writes slightly. Every fast MongoDB app is a well-indexed MongoDB app.

Understanding the topic

• Index = B-tree on one or more fields.
• Every collection gets a unique index on _id automatically.
• You add others as your query patterns emerge.
• Indexes live in RAM for hot data — sizing matters.

Syntax reference

db.users.createIndex({ email: 1 }, { unique: true });
db.users.getIndexes();