Lesson 12 / 22
Indexes
Speed up queries by avoiding a full collection scan.
Why indexes matter
Without an index, MongoDB scans every document to find matches. An index is a sorted structure that lets it jump straight to the right documents.
Creating an index
1 means ascending order, -1 means descending.
db.users.createIndex({ email: 1 })Checking the query plan
explain() shows whether a query used an index scan (IXSCAN) or a slower collection scan (COLLSCAN).
db.users.find({ email: "ada@example.com" }).explain("executionStats")Indexes aren't free
Each index speeds up reads but slows down writes slightly and uses extra storage — index only the fields you actually query on.