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Twitter System Design

Twitter Design

Functional Requirements

Scope, Priority

  1. A user should be able to post tweets

    • A tweet can be 124 characters long
    • A tweet can attach a picture
    • A tweet can attacha video

  2. A user should be able to retweet

  3. A user should be able to Like, Comment on a tweet and share a tweet

  4. A user should have access to a feed.

    • The feed can be ordered by latest
    • The feed can be ordered by most relevant

  5. A user should be notified when a tweet is received

  6. A user should be notified when the feed has new content

  7. A user should be able to search other users, tweets

  8. A user should be able to receive notifications

  9. A user should be able to follow other users.

  10. Any user can access another users Page and see the latest Tweets, Replies, Likes for that user.

  11. A user should be able to change their setting. (name, bio description, picture...)

  12. A user should be able to send private message and receive private message

Priority 1-10 message12, settings11

Users: 1B Average post per day: 5 post per day per user (User with more or less) Average news feed lookup: 5 times per day per user

Non-Functional Requirements:

  1. Scalability
  2. Availability (Up 99.999 9.9999. 1 minute per year down)
  3. Fault-Tolerant
  4. Performant (Fast)
  5. Cost??

Back of the Envelope Estiamtions

Users 1B -userid -username -bio description ...

Tweets -tweetid -content -resource -resoruceType(IMAGE,PICTURE,LINK)

Followers (Graph DB... Distributed Graph) -followeruserid -followeduserid

Notification -userid -message

Feed -userid -listofposts -creationdate -status (NEW, PARTIALY_READ, FULLY_READ)

1B * ~1000 Characters * 4 Bytes = 4TB for user

1B * 5 * 200 Characters = 1TB per day of new Tweets

Followers ... TB

Each user has 100 followers... = 1B * 100 * 100 Characters * 4 Bytes = 40TB per day

(possibly a smaller message)

https://excalidraw.com/#room=091568d066429fb3ec86,aBjTYNhjpOhC4eF62_7bCg

References:

-Grokking the System Design - Design Gurus

-System Design Interview - Alex Xu

-Designing Data Intensive Applications- Martin Kleppmann

-Funamentals of Software Architecture - Neil Ford, Mark Richards

-Software Architecture the Hard Parts - Neil Ford, Mark Richards

-System Design Primer - https://github.com/donnemartin/system-design-primer

-Blog Article https://medium.com/geekculture/cracking-the-system-design-interview-theory-basics-c57f5326181b

-Youtube