Design Twitter

Design Twitter

200 million daily active users (DAU), 100 million new tweets every day.

How many favorites per day?
200M users * 5 favorites => 1B favorites
How many total tweet-views will our system generate?
200M DAU * ((2 + 5) * 20 tweets) => 28B/day
Storage Estimates
100M * (280 + 30) bytes => 30GB/day
Bandwidth Estimates. Since total ingress is 24TB per day, this would translate into 290MB/sec.

write, new tweets, 100M/86400s => 1150 tweets per second
read 28B/86400s => 325K tweets per second.

Database Schema.

table: tweet, user, user_follow, favorite(tweet_id, user_id)

What database will you choosing between SQL and NoSQL databases?
- query performance, easy to maintain, reliability. etc.

7. Data Sharding

How to shard our data to distribute our data onto multiple machines such that we can read/write it efficiently?
user_id,
tweet_id,
tweet_create_date,
..

8. Cache

Which cache replacement policy would best fit our needs?

How can we have a more intelligent cache?

What if we cache the latest data?

hash table + doubly linked list: owner_id + tweet_id(s)

9. Timeline Generation
see facebook newsfeed.

12. Monitoring

What metrics/counters can be collected to get an understanding of the performance of our service?

13. Extended Requirements

How do we serve feeds?
Trending Topics?
Who to follow? How to give suggestions?