At the end of last year (2018), I wanted to explore opportunities and finally got the offer from PingCAP, Toutiao and Oral offer from Ant Financial. I thought I could sum up my experience and share my journey of “riding a donkey to find a horse”. Of course, one’s opinion is inevitably superficial. If there is something wrong, please correct it.

If you are interested in only one company, you can skip to it:

• Preparation process
• Interview: PingCAP
• Interview: Ants
• Interview: Headlines
• conclusion

Preparation process

I have worked for my old company for more than two years after I graduated from college. My old company is a “small company “(after all, there is no BAT or TMD title in this year, I am embarrassed to report my background). I have not worked in a big factory for more than two years after graduation, so it is very, very empty when I look for a pit. In a panic, I thought for a while to cheer myself up. The process of actually finding a hole and preparing for an interview can be divided into several stages:

• Introspection: do you really want to quit? If not, what should you do in your old employer to continue to improve?
• Positioning: Where are my strengths in hard skills (coding, architecture)? What are my strengths in soft skills (communication, teamwork)? This step along with writing a resume
• Look for platforms: which platforms can satisfy both: 1) challenges and room for improvement; 2, in line with my positioning direction; 3. The team atmosphere is as good as (or better than) the old team
• Looking for someone to push inside: basically is in v2 to find (sincere thanks to everyone to help me push inside big guy)
• The interview talk about offer

In fact, it took me several days to locate this step. First, I sorted out my project experience and expertise in the work content, and took Java + Golang as my “hard signature”, having done a wide range of business (business, middleware and infrastructure) and having expertise and interest in K8S cloud native. Then I set myself as a “soft brand” with strong learning ability, like communication and cooperation, and eager for challenges. Finally, I positioned myself as a “strong learning ability and research ability demonstrated in the past experience, but eager for challenges and unwilling to stay in the comfort zone” (shame on you!!). .

In this process, my methodology is “perspective-taking”. I have interviewed a lot of people myself (so the company usually asks me to interview, although it is a bit hard, but it is also accumulated), and I have also talked with HR and the business side that released HC about what kind of people we want to hire. Therefore, the whole process is to examine themselves in the interviewer’s mind:

If I were an interviewer, what kind of people would I hire as colleagues?

To give you a few examples, here are some of the questions I’ve considered along the way (just to my taste, of course) :

• What do I look for in a person who has graduated more than two years? In fact, people at this stage are still “empty cups”. I hope that he has strong learning ability and initiative to cultivate a super productivity for his department.
• What makes me “hate a resume” : highlighting every item in all caps, especially when the details are not focused; List the capabilities of frameworks when they are used for a class of scenarios that they feel can solve a class of business and so on;
• What questions would I prefer to ask in an interview? Languages and middleware that are “understood” or “proficient” on the resume; The second is the interesting projects on the resume, which are not fully explained;

After positioning, THE next position I wanted to find was basically locked in the direction of PaaS, cloud native and middleware. The next step is to find a pit. During this period of time, “Winter theory” is very hot, good pit is really difficult to find. Finally, I went round and round to find four internal promotion: Shopee (Singapore), PingCAP, Toutiao, ant. It was a pity for Shopee that they only received a reply to an appointment at the beginning of January after sending out their resume in early December. At that time, other interviews were nearing the end, so they chose to reject them.

After sending out the resume of these several, I focused on the resume “buried several pits”, that is, I wrote “understand and master” language and middleware and specifically used to seduce the interviewer to ask the project to review again. Later found that this step is very key, a lot of knowledge if you do not review the content really forget all, this is also calculated at the last minute, not fast light bar.

Let’s get down to business and talk about our interview experience one by one:

• Pingcap-cloud direction
• Ant-container Scheduling Direction (CTO line)
• Headline – Engineering performance direction

PingCAP

Before the interview

PingCAP’s resume response was the fastest. HR contacted me the next day after the internal promotion. After the telephone was connected, there was a brief talk about life, and then there were three social recruitment questions [” Why did you leave your job?”,” How is your salary now?”,” How is your salary expected?”]. God knows this was the first phone interview I’ve had since I started sending out resumes. I hadn’t prepared any questions like this before. In addition, I have been greatly impressed with your company ☺️”,” MY salary is XXX now, but our company has XXX besides base and I will raise my salary 🤪”,” actually I prefer platform and challenge to salary (dog head), but I still hope XXX 🤑” for basic salary requirements] so as to cope with the mud. After a little peace of mind, my sister told me about the structure and main business of my department, and then explained the following interview process. She made an appointment with me and added wechat.

“One side” is in quotation marks, because “one side” actually arranged a small project on wechat, and then appointed a time to check it.

I would like to express my special thanks to the HR sister in PingCAP. After adding wechat, she helped me coordinate the interview time and answered all kinds of strange questions. Finally, she prepared a surprise for me when talking about the offer. Interview experience directly full of stars <3!

One side

Second interview

The second interview was with me, a Cloud senior, who spent more than 50 minutes on wechat voice chat:

• I asked about my project experience and talked about two projects
• How about Kubernetes? Have you read the source code?
  • In fact, I only read kubelet about k8S code before. I read apiserver, Scheduler and Controller-Manager all at the last minute, and my smile gradually appeared.
• What is Kubernetes Service concept, how to implement?
• You were talking about Informer, how is Informer implemented and what does it do?
• Have you ever used StatefulSet? What are the characteristics?
• How is the rolling upgrade of StatefulSet implemented?
• Now we want to upgrade only any node in StatefulSet for testing. What can we do?
  • Later, when I remembered a new StatefulSet, the data in PV was lost. In fact, the correct way was to use partition mechanism, and the smile gradually disappeared.
• All resources in Kubernetes have version numbers specified.
  • For the second uncertain question, I repeatedly told myself before the interview that “don’t force me to answer” and “if I don’t know the question, I will talk about the idea”. Therefore, I said that I had never read this code, but according to the design concept of micro-service API, the version number has different functions. The answer seemed to satisfy the interviewer, so he dug down:
• How many sets of code does the K8S server need to maintain if there are more than one version number?
  • I don’t know how to write the k8S code. I can’t be sure. Holy shit), but if I were writing the code (pretending to be confident), I would just maintain a copy of the latest Model, and then design a version of Adpater to translate the old Model blah, blah, blah.” At this point, I’m a dead end
• OK, let’s talk about Golang.
• See if there is a problem with this code. Why?
• How is Goroutine scheduled?
• What is the relationship between Goroutine and kernel threads?
• Is there anything you want to ask me?

After the face of the general feeling of the answer, the in the mind a little uneasy. Results the next day HR little sister came to arrange three sides, a long sigh of relief.

On three sides

All around

When I arrived at the scene, two interviewers chatted with me for about 40 minutes:

• About the details of the Configuration Center project
• Why not use ZK and write your own configuration center?
  • I was caught off guard by this question, so I had to confess: I was young at that time and wanted to brush up on experience, but later I realized that I should not repeat the wheel. Of course, the system turned out well in the end.
• How does the configuration center do service discovery? How do you do failover?
• What pits have you encountered with Kubernetes?
• What changes have been made to Prometheus?
• What changes have been made to Alertmanager?
• How does the monitoring system do “self-monitoring”?
• How to monitor cross-room network problems?
• Is there anything you want to ask us?

Four sides is pure project, the experience inside is not quite universal. But there was one detail, and at the midway point the two interviewers checked each other out and said, “Any questions?” I realized the interviewers were running out of questions, and it was only about 20 minutes (too short an interview is bad smell). I tried to be as specific as possible about the following surveillance questions, while also mentioning that “there’s another area where we were doing a lot of work at the time”, hinting that the interviewer was looking for clues. I don’t know if it worked, but it was a close call.

Five surface

PingCAP summary

Some subjective evaluations:

• Interview difficulty: Normal
• Interview experience: I give full marks
• Question preference: Project experience, engineering ability

I really want to say a word about PingCAP (because the interview experience was great!). . The original intention of joining PingCAP is to feel that the team has a strong engineer culture, and there are many talents in it. Meanwhile, TiDB is excellent, and THE model of open source project is recognized in my heart. But there are many companies that sell dog meat, many JD write that engineers have a strong culture, in fact, many are not so true. However, after five rounds of interviews with PingCAP, I truly felt the engineer culture: there were no “tough questions” in the interview. Every interviewer was interested in my engineering thinking, learning ability and technical insights, and was very keen to discuss and dig some holes and make technical decisions with me. It feels good: the interviewer knows me, and my thinking and technical insights as an engineer are recognized and respected. It’s an atmosphere that can’t be sloganized, because it’s a hard requirement that everyone in this group has a passion for technology and a lot of engineering experience.

The ants

Before the interview

Ant’s interview is quite unique. There is no HR appointment for each round of interview. Generally, the interviewer calls at around 8 PM to ask if the interview is available.

Six interviews, the first five technical interviews, telephone interviews, the last one is HR interview, on-site interview.

One side

Second interview

• We talked about the project first
• What changes were made to Prometheus?
• Self-research configuration center, what specific content did?
• Have you used any advanced features of MySQL?
  • I asked what was an advanced feature, and the interviewer moved on to the next question
• How is the core data table in the configuration center designed?
• Why use Redis in business, what are the advantages of Redis?
  • Single thread: concurrency safety; High performance; Rich primitives and data structures; Widely used, low cost of stepping pits
• Are you familiar with Redis data structure implementation?
  • Said a zset skip list
• What data structures have you used in Redis and in what scenarios?
• What parameters can be configured to initialize a thread pool in Java?
• What JVM parameters have been tuned by your Java application, and why?
  • I only know the basic things like Max heap min heap, open G1, open GC log and OOM Dumper
• Do you have any parameters when you use Jetty, and why?
• Would it be okay if the Jetty QTP wait queue was configured to be infinite? Will there be any problems?
• Which Linux Bash commands have you used and what do you use them for?
• A pen test: need to answer in the link given, can’t Google, can’t jump out, can’t use IDE:

The title goes like this:

Start two threads, one output 1,3,5,7… 99, another output 2,4,6,8… 100 last STDOUT output 1,2,3,4,5… 100

Me: I’ll do it with Go

Interviewer: No, use the Notify mechanism of Java

Me: (not realizing the severity of the problem) I’ll use Java BlockingQueue

Interviewer: No, please use Java wait + Notify mechanism to implement

I haven’t written wait + notify at all. You can’t write ‘go’

Finally, I realized a version with Go Channel, but I couldn’t run the code on the web page I gave, and I didn’t know if it was written correctly. Then the interview ended.

This time, the interviewer continued the style of the first interview, rushing to the next question after one question, without seeming interested in or recognizing my answers. So after this round, I feel dead again…

On three sides

All around

• Introduce yourself
• How do you feel about your basic knowledge
• What data structures do you usually use?
• What are the advantages and disadvantages of linked lists versus arrays?
• How to determine if two acyclic singly linked lists have intersections
• How can I tell if two singly linked lists have an intersection
• How to determine whether a single linked list has a ring, and find out the ring point
• What is the difference between TCP and UDP?
• Describe how TCP waves four times
• The status of TCP
• What is the LISTEN state of TCP
• What is the CLOSE_WAIT state of TCP
• How to set up a socket connection
• What are the common HTTP status codes
• What’s the difference between 301 and 302
• What’s the difference between 504 and 500
• What’s the difference between HTTPS and HTTP
• Write an algorithm problem: hand type

This round of basic knowledge of the whole question, the foundation of a solid word no problem, but personally feel a bit like the school recruitment of the question.

Five surface

Six sides

I’ve heard before that ali department HR is here to “smell” (see if you fit ali’s style) and has veto power. So it’s kind of stressful.

• Ask experience
• Why would you consider coming out?
  • Golden sentence: “now their own technology growth a little encountered bottleneck, plus has been admiration for your company ☺️””
• What is the company’s main business now? (This is a lot of technical questions, I feel like I want to test my ability to explain complex problems)
• Are you bringing anyone now? What is the report level?
• Are you satisfied with your experience these years?
• What weaknesses do you see in yourself?
• Have you encountered anything frustrating?
• What are your future career plans?
• When looking at an opportunity, do you consider salary, platform, people or other factors?
• How are you being paid now
• Is there anything you want to ask me

The whole conversation lasted for more than 40 minutes, and the topic was quite broad. The interviewer also said that the pressure in System Department was great, and only the excellent people could stay. Personally, I don’t think HR has anything to prepare for except the part about salary. Just say what you want. Because when you go to HR, at least it proves that there is no problem with your skills, and speaking out is convenient for HR to judge whether the values on both sides are in accordance with each other. If they are really not in accordance with each other, it is better to fail in HR than regret and change jobs after entering, because after all, people do not like resumes that frequently change jobs.

summary

headlines

Before the interview

Toutiao will make an appointment with HR before each interview and send a ZOOM address in advance. The three technical interviews and one HR interview are all video interviews. I have to say that the video interview experience is much better than the phone interview experience (especially for people like me who pay close attention to the response of the interviewer). If HR students read this article, they should consider video interview instead of phone interview, which will be more efficient.

All three of the headlines have a similar technical style:

1. Ask for projects and pick out areas or scenarios in which you excel
2. Ask system design questions, each question will continue to deepen the requirements for you to adapt and weigh
3. Ask an algorithm problem, first look at the idea, and then ask to write pseudo-code to see if the boundary conditions can be passed once

I myself have been using this interview process, especially the system design and the constant change of requirements, which can comprehensively investigate the basic skills and engineering thinking of the back-end. So the headline interview routine is right up my street, and I’ve even asked many of the same questions myself.

One side

Second interview

• What is the usual tool chain and technology stack
• Has Golang ever stepped on a pit?
  • Answered the go-routine closure capture question in the for-range in the PingCAP interview
• Is there a bug in this Golang code (or a for-range pit)?
  • There is a bug, for-range value reference copy problem
• How to resolve the storage, collision, expansion, and concurrent access of HashMap in Java
  • Hash table, zipper method (length greater than 8 to red and black tree), double rehash, concurrent access insecure
• What are the advantages and disadvantages of the zipper method when the linked list is too long to transform into a red-black tree?
  • Advantages: Faster O(LogN) read speed; Disadvantages: Overhead during insertion, O(LogN) insertion, rotation maintenance balance
• Where is the concurrency insecurity in HashMap?
  • The zipper method resolves conflicts. It is unsafe to insert a linked list, and concurrent operations may cause another insert to fail
• Is there any special treatment for read and write operations in HashMap expansion?
  • I don’t know
• How is ConcurrentHashMap concurrency safe?
  • Segment section lock
• What locking mechanisms do Java have and what are their features?
  • Synchronized, reentrant lock
• Do you know CAS? How is CAS implemented in Java?
  • Compare and Swap, an optimistic implementation of locking, can be called “lock-free”. CAS needs to call the instructions of the corresponding OS to ensure atomicity, which cannot be implemented by JVM itself.
• What is the storage engine used by MySQL? Why InnoDB?
  • Almost all companies use MySQL to use InnoDB, to reduce the cost of trampling; Clustering index, MVCC
• What is the difference between MySQL clustered index and non-clustered index?
  • Leaf nodes of clustered indexes are data nodes (such as primary key indexes when primary keys are defined), and non-clustered index leaf nodes are Pointers to data blocks
• What are the differences between B+ trees and binary trees?
  • A B+ tree is a multi-fork tree with smaller depth. A B+ tree can traverse leaf nodes sequentially, and a B+ tree can make better use of disk sectors. Binary tree: easy to implement
• Design the index for a scene, forget the specific scene, anyway is looking at the knowledge of joint index and column selectivity
• There is a new query scenario. How to solve it?
• A in () AND B in ();
  • Select * from (A,B) in ((1,2),(3,4)); select * from (A,B) in (1,2);
• MySQL > select * from A in () AND B in ();
  • First, a non-clustered index is used to search for travel data, and then another column is used to filter
• MySQL > query A in (); MySQL > query A in ();
  • I don’t know. Those who know can leave a message
• What data structures have you used in Redis? How is ZSET implemented?
  • Jump table
• Zrange start, stop, total length n, what is the complexity?
  • O(logN) (答得不好，实际是 O(M+log(N)), M 是结果集基数 stop-start)
• How do Kafka consumers do message reduplication?
  • MySQL de-heavy, Redis de-heavy, if the scene is very large and allows misjudgment, bloom filter can also be used
• Introduce Kafka’s ConsumerGroup
  • Quite long, slightly
• How about Kubernetes and Docker? (ME: Preaching in the company)
• Did you contribute code to them? (Me: No…)
• What is the storage structure of a sequential database?
  • The storage structure of Prometheus 1. X and 2. X is described
• LSM tree? What kind of storage structure is it?
  • RocksDB, HBase, Cassandra are all used in the Log Structured Merge Tree. The structure of the Tree is forgotten, but it only says to write memtable first and then brush disk as Sstable
• Have you used Cassandra and RocksDB in production? How much is it?
  • Yes, Cassandra stores the call chain, RocksDB does the local state store for Flink and Kafka Stream
• What is Cassandra’s tombstone mechanic?
  • I don’t know, stay in the use phase for Cassandra

The second face asked a lot of basic knowledge of middleware, and finally did not have time to ask the algorithm. Java HashMap, locking mechanism, CAS index to MySQL, Redis zset, and LSM tree are all popular backend or middleware related interview questions. Of course, these questions are popular for a reason. Even if the candidate has prepared for them, a little more detail can quickly tell whether the candidate really understands or just read the relevant materials.

On three sides

HR side

Similar, ask about experience, reason for leaving, career plan, salary, expectations.

summary

conclusion

Looking back at the interview process, there were many unsatisfactory things, but finally I was lucky to get three offers. Finally, some supplementary summaries:

Some lessons:

• Be prepared for projects on your resume and areas of “mastery” or higher proficiency and middleware. When an interviewer asks you a wide range of questions, he or she doesn’t expect you to answer them. When an interviewer asks you a question about your resume, if you can’t answer it, the interviewer will think that the person is either too low in vision and thinks he has mastered it after a little bit, or lying about his resume, both of which are very unfavorable.
• Build on the above tip and prepare a favorite project that you can point to on your resume and during the interview.
• Come into the interview with a methodology in mind: Identify the qualities the interviewer is looking for in the candidate, and try to reflect those qualities during the interview. This may sound like truenonsense, but there are so many factors in the interview process that you can’t control, and having a clear goal in mind can help you figure out what to say when you feel overwhelmed. For example, in one round, when the interviewer asked me if I had any questions, I asked about the technical challenges that the corresponding positions in your company would face (of course, it should be made clear that this is not to argue that they do not have challenges, but that they are eager for challenges).

Some information and insights in various fields:

• System Design Primer, a must-see guide to architecture Design. Keep in mind that the essence of architectural design is to use engineering experience to make the best trade-offs with a deep understanding of the business scenario. One way of doing an interview is to outline what you are giving up in exchange for it.
• Cloud native, Kubernetes Concepts section recommends looking again, Aggregation layer, kubelet pod state synchronization, scheduler scheduling, and Sample Controller controller
• For language, I recommend Effective Go, Effective Java, both very thin. I have read these two books before, so I did not prepare language for the interview.
• Algorithm related, this part OF my pure tanager, to tell the truth, I think the university textbook “data structure and algorithm analysis” is written very good… As for Leetcode, I did not brush it before the interview. Recently, IN order to practice Rust, I have brushed more than 60 questions, but I did not come across any questions that appeared in the interview. It seems that if you want to brush Leetcode, you have to go through more and brush more, and brush less and try hard to achieve strong luck.
• Golang for Range: Two rounds of interviews covered this topic, posted here;

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