CHAPTER 4: DESIGN A RATE LIMITER 设计速率限制器

In a network system, a rate limiter is used to control the rate of traffic sent by a client or a
service. In the HTTP world, a rate limiter limits the number of client requests allowed to be
sent over a specified period. If the API request count exceeds the threshold defined by the
rate limiter, all the excess calls are blocked. Here are a few examples:
• A user can write no more than 2 posts per second.
• You can create a maximum of 10 accounts per day from the same IP address.
• You can claim rewards no more than 5 times per week from the same device.

CHAPTER 3: A FRAMEWORK FOR SYSTEM DESIGN INTERVIEWS 系统设计访谈的框架

You have just landed a coveted on-site interview at your dream company. The hiring
coordinator sends you a schedule for that day. Scanning down the list, you feel pretty good
about it until your eyes land on this interview session - System Design Interview.

System design interviews are often intimidating. It could be as vague as “designing a wellknown product X?”. The questions are ambiguous and seem unreasonably broad. Your
weariness is understandable. After all, how could anyone design a popular product in an hour
that has taken hundreds if not thousands of engineers to build?

CHAPTER 2: BACK-OF-THE-ENVELOPE ESTIMATION 粗略估计

In a system design interview, sometimes you are asked to estimate system capacity or
performance requirements using a back-of-the-envelope estimation. According to Jeff Dean,
Google Senior Fellow, “back-of-the-envelope calculations are estimates you create using a
combination of thought experiments and common performance numbers to get a good feel for
which designs will meet your requirements” [1].
You need to have a good sense of scalability basics to effectively carry out back-of-theenvelope estimation. The following concepts should be well understood: power of two [2],
latency numbers every programmer should know, and availability numbers.

作者简介

About the author:
Alex Xu is an experienced software engineer and entrepreneur(/ˌɑːntrəprəˈnɜːr/). Previously, he worked at
Twitter, Apple, Zynga and Oracle. He received his M.S. from Carnegie Mellon University.
He has a passion for designing and implementing complex systems.

作者简介：Alex Xu是一位经验丰富的软件工程师和企业家。此前，他曾在Twitter，Apple，Zynga和Oracle工作。他在卡内基梅隆大学获得硕士学位。他对设计和实施复杂系统充满热情。

CHAPTER 1: SCALE FROM ZERO TO MILLIONS OF USERS

Designing a system that supports millions of users is challenging, and it is a journey that
requires continuous refinement and endless improvement. In this chapter, we build a system
that supports a single user and gradually scale it up to serve millions of users. After reading
this chapter, you will master a handful of techniques that will help you to crack the system
design interview questions.