Kavya's campus noticeboards
Kavya builds Campus Buzz, a social app for her college. Students follow each other, post updates, and open the app to see a home feed. (Kavya, the app and every number here are made up for teaching.)
She pictures every student with a personal noticeboard. When a friend posts, there are two ways to get the post onto your board:
- Pin a copy on every follower's noticeboard right away. Readers just glance at their own board. Reading is instant, and writing is expensive.
- Leave the post on the author's desk. Each reader walks round collecting from everyone they follow. Writing is cheap, and reading is expensive.
Real feeds use both, and the choice depends on how many followers an author has. That is the heart of the news-feed interview. Each section below starts with a complaint Kavya actually gets:
| Complaint |
Idea it forces |
| "The feed takes four seconds to open" |
Fan-out on write (push) |
| "The cricket star joined and the app fell over" |
The hybrid and the celebrity problem |
| "The follower-count page is killing the database" |
Graph storage and async counters |
| "My best friend's post is buried under lunch photos" |
Ranking |
| "I see the same post twice when I scroll" |
Cursor pagination |
| "I deleted it, but it's still in people's feeds" |
Read-time filtering |
| "Ranking went down on fest night" |
Graceful fallback |
This guide extends the fan-out ideas from Chat and notifications and the case study on professional networks.
1. What Campus Buzz must do
- Functional: publish a post, follow and unfollow, and read a ranked home timeline of recent posts from the people you follow.
- Non-functional: the timeline loads in a couple of hundred milliseconds, new posts appear within seconds, and staying available matters more than perfect consistency.
You've reached the free preview of this post.
Subscribe to the Blogs plan (₹99/mo) — or use any Algomi Suite, Career, Investor, or Trader plan — to keep reading.
See plans
