System Design Twitter

interviewers really want is high-level ideas about how you will solve the problem.
how you define the problem
how you design the solution
how you anlysis the issue step by step are truly important
8 Things You Need to Know Before a System Design Interview

making problem clearer and more concrete
only design core features of Twitter instead of everything.
- the whole product should allow people follow each other and view others feeds.
registration, moment, security is out of the scope

don’t jump into all the details immediately
to divide the whole system into several core components
- frontend/backend, offline/online logic
following two things:
- Data modeling:
  - define user object and feed object
  - releations are also necessary
- How to serve feeds
  - way is to fetch feeds from all the poeple you follow and render them by time.

Q. When users followed a lot of people, fetching and rendering all their feeds can be costly. How to improve this?
A.
- infinite scroll feature, to fetch the most recent N feeds instead of all of them.
- consider cache, which might also be helpful to speed things up.
Q. How to detect fake users?
A.
- features(e.g., registration date, the number of followers, the number of feeds), build a machine learning system to detect if a user is fake
Q. Can we order feed by other algorithms?
A. (should clarify)
- How to measure the algorithm?
  - by the average time users spend on Twitter
  - users interaction like favorite/retweet.
- What signals to use to evaluate how likely the user will like the feed?
  - Users relatio nwith the author, the number of replies/retweets of this feed,
Q. How to implement the @feature and retweet feature?
A. We can simply store a list of user IDs inside