March 25, 2026

Interview Question:

Your query returns just 20 rows…
but it takes 3 seconds in production!

How do you make it under 1 millisecond?

This is not about coding.
This is about efficient database design and query optimization.

At this scale, OFFSET kills performance if design is weak.

Here’s how you fix it in production:

⸻

1️⃣ Avoid OFFSET for Deep Pagination

OFFSET scans all previous rows → slows down queries.
Large OFFSET values = disaster in production.

Example of slow query:
SELECT * FROM customer ORDER BY id LIMIT 20 OFFSET 900000;
2️⃣ Use Indexed WHERE
Filter with indexed columns instead:
SELECT * FROM customer WHERE id gt 900000 ORDER BY id LIMIT 20;

Execution: 3s → ~2 ms
• No full scan, database jumps directly to rows

3️⃣ Database Lessons

• OFFSET is okay for small pages, never for deep pages
• Always leverage primary key or indexed columns
• Proper indexing and query patterns = scalable production

⸻

🔥 Interview Ready One-Liner:

Deep pagination kills queries,
but filtering + indexing = lightning fast results.

Comment “DB Fast” for full production optimization guide.

#backend #sql #database #queryoptimization #scalability microservices performance softwareengineer

Видео March 25, 2026 канала CodeEra by Amit