Why are database indexes important, and what are potential downsides?

Why are database indexes important, and what are potential downsides?

• A. They speed up queries but incur write overhead and storage costs.
• B. They slow down reads but speed up writes.
• C. They encrypt data to enhance security.
• D. They prevent SQL injection without any overhead.

Answer: (A)

Indexes organize pointers to rows so the database can jump directly to relevant data instead of scanning every row. This makes read operations, especially those that filter on indexed columns or perform lookups, much faster because the engine can locate results without a full table sweep.

But that speed comes with tradeoffs. Each index needs to be updated whenever data changes, so inserts, updates, and deletes carry extra work to keep the index in sync. That write-time overhead can slow down writes. Additionally, the index itself consumes storage space beyond the table data. Put together, you get faster reads at the cost of slower writes and extra storage.

This matches the idea that they speed up queries while adding write overhead and storage costs. Other choices mix in security features—encryption or protection against SQL injection—which are separate concerns and not what indexes do.