Q: How would you design Google Drive?

**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

Q: How would you design ad click event aggregation?

**Target Audience:** Intermediate engineers preparing for system design rounds — you know what a queue and a database are; every streaming term is defined when it first appears. **Difficulty:** Hard **Verified with:** Node 22.22, Python 3.12, Go 1.24 and Java 21 (all four print identical output). Traffic figures are stated assumptions. Apache Flink windowing behaviour (allowed lateness, late-data side outputs) is from the Flink windows documentation, checked October 2026. > **How to read this d

Question 1

What is the difference between strong and eventual consistency?

Accepted Answer

**Target Audience:** Beginners to distributed systems — you know what a database and a replica copy are; everything else is defined as we go.
**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. Stale-read rates and timings come from the example program; the **Verified** section

Question 2

How would you design a news feed system?

Accepted Answer

**Target Audience:** Engineers preparing for a senior system design round. You know what a server, a database and a cache are; feed-specific ideas are defined as we go.
**Difficulty:** Hard
**Verified with:** Node 22.22 and Python 3.12 (both print identical output). Product facts are cited inline and were checked in October 2026.

> **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 expects.

Question 3

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 4

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 5

How would you design Instagram?

Accepted Answer

**Target Audience:** Engineers preparing for a system design round. You know what a server, a database and HTTP are; storage, CDN and sharding ideas are defined as we go.
**Difficulty:** Hard
**Verified with:** Node 22.22, Python 3.12, Go 1.24 and Java 21 (all four print identical output). Instagram engineering facts are cited inline, checked in October 2026.

> **How to read this doc:** Plain language first, then `📌 Interview term:` callouts. Numbers come from the example program and are quote

Question 6

How would you design Twitter's timeline and search? (Facebook feed)

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** posts a tweet — 280 chars + media refs, persisted, then fanned out to followers' timelines.
- **User** reads home timeline — GET merged, ranked feed (paginated, <200ms p95).
- **Service** searches tweets — inverted index over tokens/hashtags with ranking and recency.
- **Service** fans out / backfills — asy

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 ad click event aggregation?

Accepted Answer

**Target Audience:** Intermediate engineers preparing for system design rounds — you know what a queue and a database are; every streaming term is defined when it first appears.
**Difficulty:** Hard
**Verified with:** Node 22.22, Python 3.12, Go 1.24 and Java 21 (all four print identical output). Traffic figures are stated assumptions. Apache Flink windowing behaviour (allowed lateness, late-data side outputs) is from the Flink windows documentation, checked October 2026.

> **How to read this d

SYSTEM DESIGNDECODED.

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