Question 1

What is database sharding?

Accepted Answer

**Target Audience:** Beginners to system design who know what a database table is; no distributed-systems background assumed.
**Difficulty:** Medium
**Verified with:** Node 22.22 and Python 3.12 (both print identical output). Notion figures are cited from the Notion engineering blog; DynamoDB limits from the AWS DynamoDB developer guide.

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the words an interviewer e

Question 2

How would you design a ticket booking system like Ticketmaster?

Accepted Answer

**Target Audience:** Backend engineers preparing for the "design Ticketmaster" round, which is really a question about contention, holds and admission control.
**Difficulty:** Hard
**Verified with:** Node 22.22 and Python 3.12 (identical output). The Eras Tour figures are from Ticketmaster's statement of November 2022 as reported by CBS News and Cox Media Group stations.

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you als

Question 3

How would you design a distributed cache?

Accepted Answer

**Target Audience:** Intermediate — you know what a cache is and what a hash function does; distributed-systems vocabulary is defined as it appears.
**Difficulty:** Hard
**Verified with:** Node 22.22, Python 3.12, Go 1.24 and Java 21 (all four print identical output).

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact words an interviewer expects. Slot numbers, key movements and node loads come from runn

Question 4

How would you design an analytics/metrics pipeline?

Accepted Answer

**Target Audience:** Engineers who have sent analytics events from an app and want to know how they become trustworthy dashboard numbers, and candidates preparing for a data-pipeline design round.
**Difficulty:** Hard
**Verified with:** Node 22.22 and Python 3.12 (both examples print identical output in both). The Lambda/Kappa history is from coverage of Jay Kreps's 2014 O'Reilly essay "Questioning the Lambda Architecture" (HPCwire, Kai Waehner); Redis HyperLogLog size and error (12 KB, 0.81%) f

Question 5

How would you design a distributed key-value store?

Accepted Answer

**Target Audience:** Engineers preparing for the classic "design a key-value store" round, which tests whether you can combine partitioning, replication, consistency and storage into one coherent system.
**Difficulty:** Hard
**Verified with:** Node 22.22, Python 3.12, Go 1.24 and Java 21 for the cluster example (identical output); Node 22.22 and Python 3.12 for the storage-engine example. The design follows the Dynamo paper (DeCandia et al., SOSP 2007); the DynamoDB 400 KB item limit is from the

Question 6

How would you design a Web Crawler?

Accepted Answer

**Target Audience:** Engineers preparing for a system design round; no prior knowledge of crawling or search engines is assumed, and every term is defined when it first appears.
**Difficulty:** Hard
**Verified with:** Node 22.22 and Python 3.12 (both print identical output). The robots.txt standard (RFC 9309) and search engine handling of `Crawl-delay` checked against the RFC and Google Search Central in October 2026.

> **How to read this doc:** Every idea is explained in plain language first,

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