Lesson 12 / 23
Indexes
Speed up queries with indexes, check IXSCAN versus COLLSCAN with explain and balance read gains against write cost.
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.