Question 1

What is the difference between REST and GraphQL?

Accepted Answer

**Target Audience:** Beginners to system design — you have called an HTTP API; no GraphQL experience assumed.
**Difficulty:** Medium
**Verified with:** Node 22.22 and Python 3.12 (both 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. Request counts and byte sizes come from running the example; the **Verified** section quotes the full output.

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Question 2

What is the difference between horizontal and vertical scaling?

Accepted Answer

**Target Audience:** Beginners to system design — you know what a server and a database are, nothing more.
**Difficulty:** Medium
**Verified with:** Node 22.22 and Python 3.12 (the example prints the same table in both).

> **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. Every number below comes from actually running the example program; the **Verified** section quotes its f

Question 3

How does caching improve system performance?

Accepted Answer

**Target Audience:** Beginners to system design — you know what a database query is; no caching background assumed.
**Difficulty:** Medium
**Verified with:** Node 22.22 and Python 3.12 (both 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. Hit ratios, latencies and counts come from running the example; the **Verified** section quotes the full outpu

Question 4

How would you design a feature flag system (LaunchDarkly-style) at scale?

Accepted Answer

**Target Audience:** Beginners to system design — you know what a web service and a database are; every flag-system term is defined as it appears.
**Difficulty:** Medium
**Verified with:** Node 22.22 and Python 3.12 (both print identical output). The fleet, flag counts and latencies are stated assumptions; LaunchDarkly behaviour quoted below is from LaunchDarkly documentation (architecture overview and SDK contributor guide), checked October 2026.

> **How to read this doc:** Every idea is expla

Question 5

How would you design a 'nearby drivers' / proximity search?

Accepted Answer

**Target Audience:** Developers preparing for system design interviews. You know what a database index and a cache are; no maps or geometry background needed.
**Difficulty:** Hard
**Verified with:** Node 22.22, Python 3.12, Go 1.24 and Java 21 (all four print identical output). Redis behaviour and memory were checked on Redis 7.0.15.

> **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

SYSTEM DESIGNDECODED.

Medium

What is the difference between REST and GraphQL?

What is the difference between horizontal and vertical scaling?

How does caching improve system performance?

How would you design a feature flag system (LaunchDarkly-style) at scale?

Hard

How would you design a 'nearby drivers' / proximity search?