When not to index in MongoDB

Introduction

Indexes help find data faster, but sometimes they slow things down or use too much space. Knowing when not to add an index saves resources and keeps your database fast.

When the collection is very small and queries are fast without indexes.

When the field has many repeated values, so the index won't help much.

When you write data very often and indexing slows down inserts or updates.

When the field is rarely used in queries or sorting.

When storage space is limited and indexes take too much room.

Syntax

MongoDB

No specific syntax because this is about deciding NOT to create an index.

Indexes are created with db.collection.createIndex() in MongoDB.

Choosing not to index is a decision based on data and query patterns.

Examples

This means you skip db.collection.createIndex({status: 1}) to save space and write speed.

MongoDB

// No index created on 'status' because it has few unique values
// and queries on it are rare.

For small collections, scanning all documents is quick, so no index needed.

MongoDB

// No index on 'description' field because collection is small
// and full collection scans are fast.

Sample Program

This example shows a situation where you choose not to create an index on a rarely used field in a small collection.

MongoDB

use shopDB
// Suppose 'orders' collection is small and 'notes' field is rarely queried
// We decide NOT to create an index on 'notes'
// So no createIndex command is run here

// To check existing indexes:
db.orders.getIndexes()

Important Notes

Too many indexes slow down data writes because each index must be updated.

Indexes use extra disk space, so avoid indexing fields with low uniqueness.

Always monitor query performance and adjust indexes as your data grows.

Summary

Indexes speed up queries but can slow down writes and use space.

Don't index small collections or fields rarely used in queries.

Skip indexing fields with many repeated values to save resources.