Instagram Design Scratch

SystemDesign

创建时间:2020-11-16 01:59

字数:436 阅读:

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1. Intro and Instagram
2. Design

1. Intro and Instagram

social networking service
upload and share photos and videos
share info either publicly or privately
share through other social networking platforms
- facebook
- twitter
- flickr
- tumblr

requirement
- functional
  - users should be able to upload/ download/ view photos
  - search based on photo/ video titles
  - users can follow other users
  - system will generate and display a user’s News Feed consisting of top photos from all the people the user follows
- non-functional
  - services need to be highly available
  - latency come to be 200ms for News Feed Generation

2. Design

patterns
- read heavy system
  - need to effectively manage storage
  - 100% reliable of data
  - low latency

system design
- we need to support two scenarios
  - upload photos
  - view/ search photos
- db
  - image storage
  - image metadata storage

Separate read and write servers
- web servers have a connection limit
- assume max is 500 connections, that means server cannot have more than 500 concurrent uploads or reads
reliability
- run a redundant secondary copy of the service that is not serving any traffic if only one instance of a service is required to run at any point
data sharding
- partition based on UserID?
  - hot user
  - non-uniform storage as some users may upload a lot of images
  - what if one shard is full?
  - unavailability – all users data come to be unavailable all of sudden
- use photoId as partition key
news feeds - e.g 100 feeds
- real time generation
  - need to go to user follow table to get all of its following people
  - then query with user id to get their 100 updates
  - combine them, go through our ranking algo
  - then generate the output
- should choose pre-generating way as it will save a lot of times
  - have dedicated servers that are continuously generating users’ News Feeds and storing them in a UserNewsFeed table
approaches for seanding news feed contents to users
- pull
  - clients can pull the News Feed contents from the server on a regular basis or manually whenever they need it
    - problems
      - new data might not be shown to the users until clients issue a pull request
      - most of time, pull requests response could be empty
    - push
      - servers can push new data to the users as soon as it is available
      - users then need to maintain a long poll request with the server for receiving the updates
      - issue
        
        user has follow a lot of people
        
        celebrity user who has meillions of followers
        
        server then have to push updates quite frequently
    - hybrid
      - move all the users who have a high number of follows to a pull based model and only push data to those users who have a few hundred follows

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