1. Definition

Although indexing improves read performance, it is not always beneficial. In some cases, indexes can slow down operations and consume extra resources.

2. When NOT to Use Indexing

• When the collection has very small data
• When fields are rarely used in queries
• When write operations (insert/update/delete) are frequent
• When data changes very often
• When queries return most of the documents

3. Why Not to Use Indexing

• Indexes consume extra memory/storage
• Slows down write operations
• Maintenance overhead for updating indexes
• Unnecessary indexes reduce performance

4. How It Affects Performance

• Each insert/update must update indexes
• More indexes = more work for database
• Can increase storage usage significantly
• May slow down overall system

Example

// Not useful index (rarely used field)
db.users.createIndex({ randomField: 1 });

// Query returns most documents (index not helpful)
db.users.find({ age: { $gt: 0 } });

5. Best Practice

• Create indexes only on frequently queried fields
• Avoid unnecessary indexes
• Monitor performance before adding indexes
• Balance between read and write performance

Index vs No Index (When Not Needed)