Typical System Design questions
Type_1: Desgn XXX System
Type_2：Design specific components in certain system
4S 分析法
重点:
- Ask Before Design: 问清楚再动手设计，切记不要做关键词大师
- No more no less：不要想射设计最牛的系统，要设计够用的系统
- Work Solution First：先设计一个基本能工作的系统，然后再逐步优化
- Analysis is important than solution: 通过分析过程展示知识储备，权衡各种设计方式的利弊
- Scenario 场景
- Ask
- Features
- QPS
- DAU
- Interface
- Service 服务
- Slipt
- Application
- Module
- Storage 存储
- Schema
- Data
- SQL
- NoSQL
- FileSystem
- Scale
- Sharding
- Optimize
- Special Case
Scenario 场景
- 确定需要设计哪些功能
- 承受多大访问量： MAU，DAU
罗列功能
Enumerate all features
QPS analsis
Average QPS: DAU * times_user_request
Peak QPS: averaeg QPS * 3
Fast Growing system: peak user * 2
Why we need QPS?
- QPS = O(100), your laptop can serve the QPS
- QPS = O(1k), a decent server
- QPS = O(1m), web server
Service 服务
- Replay 重放需求：重新过一遍需要的每个需求，为每个需求添加一个服务
- Merge 归并需求：归并相同的服务
Major Types:
- User Service: Register, login
- Tweet Service
- Media Service
- Friendship Service
Storage 存储
- 为每个Service选择存储结构
- Schema细化表结构
Database
- Relationship Database: Need sharding
- NoSQL Database: Tweets: Append, Simple Id based
File SystemDesign
- Thumbnail, Media File
Cache
- Nonpersistent
User Table
- Integer: user_id
- String: user name
- String: email
- String: password
Scale 拓展
Optimize 优化
- 解决设计缺陷 Solve Bottle Neck：Pull V.S. Push
- 更多功能设计 More Features：Like，Follow
- 一些特殊情况 Special Cases
Maintainence 维护
- 鲁棒性 Robust
- Scalability