[译]《Grokking the System Design Interview》系统设计访谈：分步指南

这是一篇双语翻译的文章，原文出自 grok_system_design_interview.pdf 的一篇文章《System Design Interviews: A step by step guide》系统设计访谈：分步指南。

A lot of software engineers struggle with system design interviews (SDIs) primarily because of three reasons:

许多软件工程师在系统设计面试（SDI）中遇到困难，主要是因为以下三个原因：

Like coding interviews, candidates who haven’t put a conscious effort to prepare for SDIs, mostly perform poorly especially at top companies like Google, Facebook, Amazon, Microsoft, etc. In these companies, candidates who don’t perform above average, have a limited chance to get an offer. On the other hand, a good performance always results in a better offer (higher position and salary), since it shows the candidate’s ability to handle a complex system.

与编码面试一样，没有刻意准备 SDI 的候选人大多表现不佳，尤其是在 Google、Facebook、亚马逊、微软等顶级公司。在这些公司中，表现不高于平均水平的候选人获得报价的机会有限。另一方面，良好的表现总是会带来更好的工作机会（更高的职位和薪水），因为它显示了候选人处理复杂系统的能力。

In this course, we’ll follow a step by step approach to solve multiple design problems. First, let’s go through these steps:

在本课程中，我们将遵循逐步的方法来解决多个设计问题。首先，让我们完成以下步骤：

Step 1: Requirements clarifications

步骤 1：需求澄清

It is always a good idea to ask questions about the exact scope of the problem we are solving. Design questions are mostly open-ended, and they don’t have ONE correct answer, that’s why clarifying ambiguities early in the interview becomes critical. Candidates who spend enough time to define the end goals of the system always have a better chance to be successful in the interview. Also, since we only have 35-40 minutes to design a (supposedly) large system, we should clarify what parts of the system we will be focusing on.

询问我们正在解决的问题的确切范围总是一个好主意。设计问题大多是开放式的，并且没有一个正确的答案，这就是为什么在面试初期澄清歧义变得至关重要。花足够时间来定义系统最终目标的候选人总是有更好的机会在面试中取得成功。另外，由于我们只有 35-40 分钟的时间来设计一个（据称）大型系统，因此我们应该明确我们将重点关注系统的哪些部分。

Let’s expand this with an actual example of designing a Twitter-like service. Here are some questions for designing Twitter that should be answered before moving on to the next steps:

让我们通过设计类似 Twitter 的服务的实际示例来扩展这一点。以下是设计 Twitter 时应回答的一些问题，然后再继续下一步：

All such question will determine how our end design will look like.

所有这些问题将决定我们的最终设计会是什么样子。

Step 2: System interface definition

步骤2 ：系统接口定义

Define what APIs are expected from the system. This will not only establish the exact contract expected from the system, but will also ensure if we haven’t gotten any requirements wrong. Some examples for our Twitter-like service will be:

定义系统期望提供哪些 API。这不仅可以建立系统所期望的准确合同，而且还可以确保我们没有错误地提出任何要求。我们类似 Twitter 的服务的一些示例如下：

postTweet(user_id, tweet_data, tweet_location, user_location, timestamp, ...)
generateTimeline(user_id, current_time, user_location, ...)
markTweetFavorite(user_id, tweet_id, timestamp, ...)

Step 3: Back-of-the-envelope estimation

步骤 3：粗略估计

It is always a good idea to estimate the scale of the system we’re going to design. This will also help later when we will be focusing on scaling, partitioning, load balancing and caching.

估计我们要设计的系统的规模总是一个好主意。当我们稍后关注扩展、分区、负载平衡和缓存时，这也会有所帮助。

Step 4: Defining data model

步骤 4：定义数据模型

Defining the data model early will clarify how data will flow among different components of the system. Later, it will guide towards data partitioning and management. The candidate should be able to identify various entities of the system, how they will interact with each other, and different aspect of data management like storage, transportation, encryption, etc. Here are some entities for our Twitter- like service:

尽早定义数据模型将阐明数据如何在系统的不同组件之间流动。稍后，它将指导数据分区和管理。考生应该能够识别系统的各种实体，它们如何相互交互，以及数据管理的不同方面，如存储、传输、加密等。以下是我们类似 Twitter 服务的一些实体：

User: UserID, Name, Email, DoB, CreationDate, LastLogin, etc.

Tweet: TweetID, Content, TweetLocation, NumberOfLikes, TimeStamp, etc.

UserFollow: UserID1, UserID2

FavoriteTweets: UserID, TweetID, TimeStamp

Which database system should we use? Will NoSQL like Cassandra best fit our needs, or should we use a MySQL-like solution? What kind of block storage should we use to store photos and videos?

我们应该使用哪种数据库系统？像 Cassandra 这样的 NoSQL 是否最适合我们的需求，或者我们应该使用类似 MySQL 的解决方案？我们应该使用什么样的块存储来存储照片和视频？

Step 5: High-level design

步骤 5：高层设计

Draw a block diagram with 5-6 boxes representing the core components of our system. We should identify enough components that are needed to solve the actual problem from end-to-end.

绘制一个框图，其中 5-6 个方框代表我们系统的核心组件。我们应该确定端到端解决实际问题所需的足够组件。

For Twitter, at a high-level, we will need multiple application servers to serve all the read/write requests with load balancers in front of them for traffic distributions. If we’re assuming that we will have a lot more read traffic (as compared to write), we can decide to have separate servers for handling these scenarios. On the backend, we need an efficient database that can store all the tweets and can support a huge number of reads. We will also need a distributed file storage system for storing photos and videos.

对于 Twitter，在较高层面上，我们需要多个应用程序服务器来服务所有读/写请求，并在它们前面提供负载均衡器以进行流量分配。如果我们假设我们将有更多的读取流量（与写入相比），我们可以决定使用单独的服务器来处理这些场景。在后端，我们需要一个高效的数据库来存储所有的推文，并且可以支持海量读取。我们还需要一个分布式文件存储系统来存储照片和视频。

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Step 6: Detailed design

步骤 6：详细设计

Dig deeper into two or three components; interviewer’s feedback should always guide us what parts of the system need further discussion. We should be able to present different approaches, their pros and cons, and explain why we will prefer one approach on the other. Remember there is no single answer, the only important thing is to consider tradeoffs between different options while keeping system constraints in mind.

深入挖掘两个或三个组件；面试官的反馈应该始终指导我们系统的哪些部分需要进一步讨论。我们应该能够展示不同的方法及其优缺点，并解释为什么我们更喜欢一种方法而不是另一种方法。请记住，没有单一的答案，唯一重要的是考虑不同选项之间的权衡，同时牢记系统约束。

Step 7: Identifying and resolving bottlenecks

步骤 7：识别并解决瓶颈

Try to discuss as many bottlenecks as possible and different approaches to mitigate them.

尝试讨论尽可能多的瓶颈以及缓解瓶颈的不同方法。

Summary

概括

In short, preparation and being organized during the interview are the keys to be successful in system design interviews. The above-mentioned steps should guide you to remain on track and cover all the different aspects while designing a system.

简而言之，面试过程中的准备和组织是系统设计面试成功的关键。上述步骤应指导您在设计系统时保持正轨并涵盖所有不同方面。

Let’s apply the above guidelines to design a few systems that are asked in SDIs.

让我们应用上述指南来设计 SDI 中要求的一些系统。

参考文章：

如何设计一个短网址服务
[译]《Grokking the System Design Interview》系统设计主模板