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.

## 1.

Question 2

When would you choose SQL vs NoSQL?

Accepted Answer

**Target Audience:** Beginners to system design — you have used a spreadsheet or a database table; no database internals 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. Behaviour shown comes from running the example; the **Verified** section quotes the full output.

Question 3

What is the saga pattern for distributed transactions?

Accepted Answer

**Target Audience:** Developers who build or interview for microservice back ends. You know what a database transaction is; no distributed-systems 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. All behaviour shown comes from running the example; the **V

Question 4

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

Question 5

How would you design Twitter's timeline at scale?

Accepted Answer

**Target Audience:** Engineers preparing for a system design round. You know what a cache and a database are; the timeline-specific ideas are defined as we go.
**Difficulty:** Hard
**Verified with:** Node 22.22 and Python 3.12 (both print identical output). Twitter figures are from published talks and write-ups cited inline, checked in October 2026.

> **How to read this doc:** Plain language first, then `📌 Interview term:` callouts with the precise vocabulary. The cost table is computed by the

Question 6

How would you design the data structures for a social network (Social Graph)?

Accepted Answer

## Step 1: Use Cases, Constraints, Assumptions, Back-of-Envelope

### Use cases
We'll scope to handle only the core flows that expose the bottlenecks; everything else is deferred.

- **User** adds/removes friend — mutual edge write, idempotent, replicated with quorum.
- **User** reads friends / friends-of-friends — adjacency lookup, paginated, filtered by activity.
- **User** reads feed derived from graph — 2-hop traversal (friends' posts) with cache.
- **Service** suggests friends — FoF (friend

Question 7

How would you design Google Drive?

Accepted Answer

**Target Audience:** Developers preparing for system design interviews. This page builds on the [Dropbox design](/interview-question/how-would-you-design-a-file-storage-service-like-dropbox) (block sync) and the [S3-like object storage design](/interview-question/how-would-you-design-s3-like-object-storage-572x) (blob storage) and focuses on what is different: an ID-based shared tree, permissions, the change feed and uploads.
**Difficulty:** Hard
**Verified with:** Node 22.22 and Python 3.12 (bo

Question 8

How would you design Nearby Friends?

Accepted Answer

**Target Audience:** Developers preparing for system design interviews. You know what a cache and a WebSocket are; the geo indexing side is covered on the sibling page about nearby drivers.
**Difficulty:** Hard
**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. All behaviour shown comes from running

Question 9

How would you design Google Maps?

Accepted Answer

**Target Audience:** Developers preparing for system design interviews. You know what a CDN and a graph are; shortest-path algorithms are explained from scratch.
**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. All behaviour shown comes from running the e

SYSTEM DESIGNDECODED.

Medium