News feed

1. Level 1.0

Database Schema:

a. User

UserID	Name	Age
1	Jason	25
2	Michael	26

b. Friendship

FriendshipID	SourceID	TargetID
1	1	2
2	2	1

c. News

NewsID	AuthorID	Content	Timestamp
1	2	"Hello"	2015-01-10
2	1	"Hi"	2015-01-10

Why bad?

100+ friends

a. 1 query --> get friends list

b. 1 query -->

SELECT * FROM news

WHERE timestamp > xxx

AND authorID IN frientsList

LIMIT 1000

IN is slow

2. Level 2.0

a. Pull: Get news from each friend, merge them together. NewsFeed generated when user request.

b. Push: NewsFeed generated when news generated. We have anthor table to store newsfeed, may cause duplicate news.

Push: disadvantage: News Delay.

3. Level 3.0

a. Popular star(Justin Bieber)

　　Flowers 13M +

　　Async Push may cause over 30 minutes (13M+ insertions, delay too long)

b. Push + Push

　　for popular star, don't push news

　　for every newsfeed request, merge non-popular users newsfeed(push) and popular users newsfeed(pull).

4. Level 4.0

Push disadvantage:

a. Realtime

b. Storage (Duplicate)

c. Edit

Go back to Pull:

a. cache users' latest(14 days) news

b. Broadcast multiple request to multiple server (shard by userID)

c. Merge & sort newsfeed(time, forward frequency, friends' forward, dedup, sort)

d. Cache newsfeeds for this user with timestamp (user_login)