Module 01 · Machine basics · Drill

Machine basics drill

Scenario prompts that check whether machine basics is usable under pressure. Answer out loud, then compare.

4 prompts20 minNew

0 of 4 graded

Prompt 1
A service answers each request with about 200 random lookups into an in-memory hash map. With a 5 MB map it handles requests in 20 microseconds; after the dataset grows to a 40 GB map, the same code takes over 300 microseconds. Nothing else changed. Explain the slowdown with numbers and propose two fixes.
Say your answer out loud first. Thirty seconds is enough.
Prompt 2
Walk through what happens between an engineer running ./server on a Linux host and the first line of main executing. Then explain why the same service, written in Java, has a poor p99 for two minutes after every deploy, and how you would remove it.
Say your answer out loud first. Thirty seconds is enough.
Prompt 3
Review this schema and API for a payments product: order_id is a signed 32-bit auto-increment integer, amount is a double, created_at is a 32-bit Unix timestamp in seconds, customer names are VARCHAR(50) truncated by byte count, and IDs are returned to a JavaScript web client as JSON numbers. Find every representation bug and give the fix.
Say your answer out loud first. Thirty seconds is enough.
Prompt 4
A UDP-based metrics collector receives about 2 million small packets per second. One CPU core sits at 100 percent in kernel softirq time, packets are dropped, and the other 15 cores are mostly idle. Explain what is happening at the interrupt level and how you would spread and reduce the work.
Say your answer out loud first. Thirty seconds is enough.