CodeSignal Technical Assessment System Design and Architecture 3

Question 1

In a distributed system, which CAP theorem combination is chosen by a system that remains available during a network partition but may return stale data?

Accepted Answer

AP (Available and Partition-tolerant)

Answer

AP systems sacrifice strong consistency to remain available when partitions occur, returning possibly stale data instead of refusing requests.

Question 2

You need to aggregate 1 billion events per day into per-user daily counts. Which architecture is most cost-effective when results are only needed by morning?

Accepted Answer

Batch MapReduce job running nightly

Answer

Nightly batch MapReduce processes the full dataset efficiently in bulk, which is far cheaper than real-time aggregation for non-latency-sensitive daily counts.

Question 3

What is the main purpose of a write-ahead log (WAL) in a database?

Accepted Answer

Ensuring durability by logging changes before applying them

Answer

The WAL records every change before it is applied to data pages, allowing recovery to a consistent state after a crash.

Question 4

An API gateway receives 50,000 requests/sec. Which rate-limiting algorithm smooths traffic most evenly without bursting?

Accepted Answer

Leaky bucket

Answer

The leaky bucket drains at a constant rate, enforcing a steady outflow regardless of incoming burst patterns.

Question 5

When sharding a database by user ID, which problem arises if a small number of users generate the vast majority of traffic?

Accepted Answer

Hot shard (hotspot) imbalance

Answer

Hot shards occur when a few high-traffic keys land on the same shard, causing uneven load that negates sharding benefits.

Codesignal Practice Test

Codesignal Practice Test

CodeSignal Technical Assessment System Design and Architecture 3