Why can adding an index make a SQL query go from 200ms to 2 seconds? Shouldn’t indexes always make queries faster?

Why can 100 concurrent users slow down an API more than 10,000 requests sent one after another? Isn’t the total workload what matters?

Why does a 5GHz Wi-Fi network sometimes perform worse than 2.4GHz? Isn’t 5 supposed to be faster?

Interviewer: YOUR DATABASE GOT SLOWER AFTER DOUBLING RAM. Before: 300ms. After: 2.4 seconds. No query changes. What would you investigate?

Interviewer: YOUR DATABASE HANDLES 10K QUERIES/SEC BUT STRUGGLES AT 2K. CPU is low. Memory is stable. Queries haven’t changed. What hidden bottleneck would you investigate?

Your SQL query returns 1 million rows. You add LIMIT 10, but it's still slow. Why? A) Missing index B) Expensive sorting C) Network latency D) All are possible

Interviewer: YOUR SQL QUERY GOT 50X SLOWER AFTER ADDING LIMIT 10. Without LIMIT: 400ms. With LIMIT: 20 seconds. How is that possible?

What makes a man genuinely happy?

Interviewer: YOUR API GOT SLOWER AFTER ADDING MORE SERVERS. 4 instances → 200ms. 12 instances → 900ms. Why?

Interviewer: YOUR SQL RETURNS 20 ROWS BUT READS 2 MILLION FIRST. What would you inspect before rewriting the query?

AI makes coding knowledge easier to access. But architecture still requires trade-offs, not answers. Does AI make senior thinking more valuable?

Interviewer: DELETE removed 5M rows, but the database size barely changed. Why didn’t the storage immediately shrink?

Interviewer: Your AI agent passes every test, but fails only in production. How would you debug a failure you can’t reliably reproduce?

ONE ENGINEER + AI CAN NOW DO MUCH MORE. Will companies hire fewer people..or expect 3× more from everyone?

YOUR INDEX MADE THE QUERY SLOWER. Without index: 400ms. With index: 1.8 seconds. How is that possible?

AI saves us hours every week. Why does nobody feel less busy?

EVERYONE SAYS “LEARN AI OR GET LEFT BEHIND.” What happens when using AI becomes as basic as using Google?

SQL FINISHES IN 70ms. Fetching the result takes 4 seconds. The query returns 600,000 rows. Is SQL performance really the problem?

Interviewer: Your query became 40x slower right after a database statistics update. No data or code changed. What happened?