# Indexes — MongoDB

Source: https://www.geekswithgeeks.com/en/mongodb/mongo-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.

```javascript
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`).

```javascript
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.