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Facebook System design

Facebook System Design

Functional Requirements

  1. A user should be able to post

  2. A user can post a Picture, Video with Text and Hashtag and Location

  3. A user can tag someone in a picture

  4. A user can set the privacy for the post

  5. A user should see a news feed

  6. A user can follow Pages and Friend other users

  7. A user can access a user Page or Friend Page

  8. A user should be able to create an account, login, logout

  9. A user can change settings

How many users ?

The system should support 1B total users? 20% of user are daily active users

How often does a user post? A user posts once a day on average

How many times a user reads the news feed and read other pages? 2 times per day and 50 posts each time

Non Functional Requirements

  1. The system should Scale to 200M users daily
  2. The system should have low latency. 200 MS
  3. The system should stay available. 99.99%
  4. The system should set privacy of account and posts.
  5. The system should be consistent in each country.

API design

Communication: REST or RPC

GET /newsFeed/{date_time}

response:

{
  [{
    post_id : 1,
    type : 'VIDEO' (or 'PICTURE'  ),
    content_url : [ {picture_id: 1, 'https://cdn.fb.com/12343'}]
    text : 'Hello',
    hashtag : ['#good','#day'],
    likes : [happy=2, angry=1],
    comments :[{
      poster_id,
      poster_name,
      comment_text
    }]
  }]
}

POST /post

request:

{
user_id,
content,
}

response:

HTTP response 200 post 201 sucess
{
status_message : 'FAIL' or 'SUCCESS'
}

POST /postContent

Body content-type: BLOB

response: HTTP response 200 post 201 sucesss

{
status: 'FAIL' or 'SUCCESS'
}

POST /follow

Body content-type: json

{
user_id_follower
user_id_follow
}

....

response: HTTP response 200 post 201 sucesss { status: 'FAIL' or 'SUCCESS' }

Back-of-the-envelope calculations

200M users daily active

200M * 2 * 50 posts = 1B * 20 = 20 B posts seen per day

Average post = 50 KB

= 100 TB read per day

(posts)

Posting 200M posts per day = 1TB per day posted

QPS read : 200M * 2 = 400M newsfeed read * 10^-5= 100K per second reads

QPS Write: 50 K per second writes

Data Design - Cache (for Latency)

newsFeed

Key * User_id (user reading)

{ [{ post_id : 1, type : 'VIDEO' (or 'PICTURE' ), content_url : [ {picture_id: 1, 'https://cdn.fb.com/12343'}] text : 'Hello', hashtag : ['#good','#day'], likes : [happy=2, angry=1], comments :[{ poster_id, poster_name, comment_text }] }]

Posts No SQL Database (for Latency and availablilty and Scalability)

post_id type : 'VIDEO' (or 'PICTURE' ), content_url : [ {picture_id: 1, 'https://cdn.fb.com/12343'}] text : 'Hello', hashtag : ['#good','#day'], likes : [happy=2, angry=1], poster_id, poster_name, comment_text

key* location or post_id

User No SQL Database user_id user_name dob created_date ... number_of_friends ... partition_key: location

Connection No SQL Database user_id followers

https://excalidraw.com/#room=7a84d23502c0446f2d8a,Ah1E7onnZ0comA3vVCC9vg

Instagram vs Facebook Difference

+Likes +Groups +Pages and People (everything is a page)

Optional: Look at difference in design Facebook vs Instagram Advertising system Recommendation of news Feed