Quiz
Check what you know, one topic at a time.
Fifteen questions on one topic, with the answer and the reason the moment you commit. Real-world scenarios, matching and ordering, not just pick-one. Every question is written from our own chapters, so you always know where to read next.
One quiz in every subject is free.
Question 4 of 15Scenario
Caching
Scenario
A link shortener serves 50,000 redirects a second. Most of them hit the same few thousand links, and the database is at 90% CPU.
What is the cheapest change that takes most of the load off the database?
- 1Add read replicas
- 2Cache the hot links in memory
- 3Shard the database by user
- 4Move to a bigger server
Correct
A few thousand hot links fit easily in memory, so a cache answers most redirects without touching the database. Replicas and sharding help too, at far more cost.
Pick a subject, then a topic
Showing 12 System design quizzes
Scaling, storage, caching, queues and the trade-offs behind them.
Core concepts
Scaling basics
Vertical and horizontal scaling, stateless services and load balancers.
Caching
Where to cache, cache-aside and write-through, invalidation and eviction.
Choosing a database
Relational or not, access patterns, indexes and blob storage.
Replication and sharding
Leaders and followers, replication lag, shard keys and hot spots.
Consistency and CAP
Strong and eventual consistency, CAP and PACELC, quorums.
Consistent hashing
Spreading keys across nodes without reshuffling everything.
Queues and streams
Decoupling with queues, logs like Kafka, delivery guarantees.
APIs and rate limiting
REST and RPC, pagination, idempotency keys and rate limits.
Numbers to know
Latency, throughput and back-of-the-envelope estimates.
Patterns
Feeds and search
Timelines, ranking, typeahead and inverted indexes.
Reliability and contention
Retries, idempotency, timeouts, locks and rushes.
How it works
Built to teach, not just to score.
Instant feedback
Commit to an answer and see right away why it is right, and why the tempting ones are not.
Real-world scenarios
A team, its traffic and its constraint: pick what you would actually do. Plus matching, ordering and choose-two.
Ask a follow-up
Still unsure? Ask about that exact question and get a short, plain answer. Part of the plan.
Quick review
Questions you miss come back later. Get one right and it is cleared from your list.
Running placement prep for a batch?
Colleges and companies can run any of these as a timed quiz round in a drive, with one link for everyone and results by subject. It is part of the seats you already have.
Questions
Good to know.
Is the quiz free?
How is a quiz marked?
Can I stop halfway?
Where do the questions come from?
Fifteen questions. About ten minutes.
Pick the topic you are least sure about. That is the one worth checking.