News Feed Design

Pull

• slow when read, but can use cache to speedup (cache the most recent 100 tweets maybe)

Push

• slow when write, but can be done async * fanout might need a few hours for a celebrity

The right approach

* Try to solve the problem with the minimum code change
    * add more machines in peak hours
* Evaluate the longterm trend to decide wether to change

Other approaches

* Push for ordinary user
* Pull for celebrity user
* Preiodically to update wether a user is celebrity

Design User System

Scenario

* register, login, search, user info update

Service

* AuthService (responsible for login and register)
* UserService (Query and store of user info)
* FriendshipService

Property

* user system: read a lot, write a little, so must use cache to speed up

Memcached

Authentication

SQL vs NoSQL

Friendship

How to scale

* sharding
* consistent hashing
* replica