“There’s no such thing as a tech debt-free system”: One PJO’s Challenge to Revamp Mercari’s Infrastructure

Mercari launched as a service in 2013, and in eight years managed to exceed 20 million monthly active users. But right now, a large-scale revamp of our development platforms is happening behind the scenes to support our front-facing growth.

We call this project Robust Foundation for Speed (RFS for short). It is meant to support disruptive growth across all of Mercari Group, by solving complex technical challenges and drastically strengthening the foundation shared across our businesses.

In this Mercan series, we interviewed four key people leading this very large-scale project. We walked through each of their careers as we took a look at their involvement in this project and why this project is happening now. Following Ken Wakasa’s interview, this time we have RFS project manager Minoru Tsuka (@mtsuka) joining us.

*The mask is removed only when taking pictures.

Featured in this article


  • Minoru Tsuka(@mtsuka)

    Tsuka gained experience operating a number of services and used it to develop the platform and build the SRE Team for a major web portal company. He joined Mercari in August 2019. After serving as engineering manager of the Microservices Platform Team, he became Director of Developer Productivity Engineering in January 2020.


A department store clerk makes his career move into engineering

ーYou were working in Yahoo! Japan before Mercari, is that right?

Yes, for about 12 or 13 years. Before that I was in a Fujitsu subsidiary called PFU, doing something similar to system integration.

ーWhat made you want to be an engineer in the first place?

My career began when I started working in a department store, actually. Computers were nothing more than a hobby back then.

ーWhy did you take up employment in a department store?

My father used to work in a department store, so I had always looked up to sales clerks. If we’re being honest, department stores sell the same items you can get in other stores, but for higher prices. Even so, they are able to sell them. I think that is because they are also selling the experience of shopping itself. That idea interested me very much.

ーYes, the location, the communication, and other various factors come together to create an experience you can’t get anywhere else. What made you change careers to become an engineer?

As you know, there was a dot-com bubble towards the end of the 90s. That made me wonder whether even I, someone without prior experience, could get a job that I could do on the computer. I got lucky and someone employed me. I asked them later why they gave me the job at the state I was in, and they said that they thought I would at least be able to do sales work in the worst-case scenario. (laughs)

ーYou obviously were an experienced sales clerk at that point.

Yes, exactly. (laughs) But once I joined, I was very obviously behind compared to everyone else around me. I was very alarmed by this and threw myself into studying. Over time I was able to handle work, and by my third year more and more clients would ask for me by name.

But our clients had clients of their own, which meant I didn’t really feel that my work was directly contributing to society at large. I reconsidered my career path and decided to change jobs. After going through screening processes for several companies, the only two left at the end were Yahoo! and Unoh (one of Mercari CEO Shintaro Yamada’s previous companies).

Minoru Tsuka(@mtsuka)

ーWhat?!

So I guess we can say I was destined to be involved in Mercari some way or another even back then. But at the time I thought Yahoo!’s area of business fit better with what I wanted to do, so I ultimately did not choose Unoh.

ーThat’s an almost unbelievable turn of fate. What sort of work did you do after joining Yahoo!?

I was deep in the infrastructure zone for 10 years, and handled almost every service. It was only in my last three years there that I took on the duty of improving the working environment for engineers.

“I don’t actually have career goals”

ーIt sounds like things were going very well for you. Why did you transfer to Mercari?

I am a fickle soul. Three years in the same job and I start feeling uncomfortable. If you put that much time into a company, you’ve probably done most of the work you’ll get to do there.

ーAnd over time you will have more and more routine work piling up.

As Yahoo!’s business areas kept expanding, I was able to take on new challenges without getting bored. Even so, as I entered 2019 I felt that I was also falling into the grips of burnout syndrome. Just then, the company had a change of presidents. I decided that was my cue to leave as well. So I quit… without finding a new job. I did freelance work for a while, received an offer from Mercari’s HR one day, and now we’re here.

ーWhat was the deciding factor for you joining Mercari?

I thought I would be able to contribute in the areas that needed my contribution. I don’t actually have career goals, or clear dreams that I strive to turn into reality. Basically all I have is the drive to help people out. This was the case even in Yahoo!. There was an executive there who had really helped me out before, and my motivation was to take on projects that would in turn make them happy.

So when I got the offer from Mercari, I first wanted to make sure that there was something I could help with. I started as a part-timer, working only 2–3 days a week.

ーAnd what did you think once you started working here?

I observed how Mercari engineers build and test their hypotheses for improving the user experience, and I found that they are very, very precise with the way they go about it. In fact, there are many engineers that make their own decisions to move their projects forward, which was a huge culture shock for me. I was worried that I wouldn’t gel well with the people here unless I first changed my own mindset.

Solve not the problem you want to, but one that the world wants you to

ーWhat has been a valuable notion to you as you’ve built up your career as an engineer?

I don’t remember who, but someone once said that engineers are problem solvers. That statement has deeply embedded itself in my mind. There are three processes to solving a problem, first of which is to discover it, second is to define it, and third is to actually solve it. If you can do these right, some value is likely to be born out of those processes.

ーValue… born?

For example, Yahoo! was focusing on smartphone businesses for a while. But simply releasing an app was not at all enough. Whatever product you make, it doesn’t have value unless it properly solves a problem faced by its users. The experience taught me that our mindset must be “solve not the problem you want to, but one that the world wants you to”. This idea also plays into the project we call Robust Foundation for Speed (RFS for short).

ーIn a previous interview you said that you uninstalled the Mercari app. Was that a means to have a different perspective for solving problems?

Exactly. Essentially, I want to contribute in ways that only I can. Of course as a Mercari employee, it is also important to use Mercari actively to contribute to the growth of GMV (gross merchandise volume). But any other Mercari member can do the same thing. It’s not part of the job description for my position specifically.

What is it, then, that only I can do? The answer I found to that question was to have the perspective of, and give feedback as, someone who hasn’t used Mercari before. So I uninstalled the app. I hope this doesn’t make anyone think that I don’t like the service we’re building. (laughs)

ーTo the contrary, I’d say you did that out of your love for it.

Indeed. I don’t know when, but one day we will enter a phase where the numbers we have to chase will be decimals of tenths, even hundredths. Then, it will be very important how we will approach people who have never used Mercari before.

As engineers, we have to consider how much those decimals will affect our traffic. And we need the adequate budget to be able to strengthen our infrastructure. If you don’t estimate things ahead of time, you can’t make the right move when push comes to shove.

This is even more important for a company considering global expansion. We will likely have at least two or three chances to experience hyper-growth like Amazon or Netflix.

ーSo you are preparing for those moments?

If you put it that way, more people may delete the Mercari app like me… so please don’t put it that way. (laughs) At least allow me to explain that I’m making up for it by having my family use the service extensively. My brother told me that he completed upwards of 300 transactions just last year.

There’s no such thing as a tech-debt free system, so we cannot allow for time-wasting conflicts

ーI’d also like to ask you about RFS. What is the scope of your involvement with this project?

Very simply put, I am something like a foreman. Or a head chef, if we’re talking restaurant terms. I have a taste of whatever comes out of the kitchen and comment on its taste, maybe even suggest a few ideas about how to rearrange the plate.

ーWhat kind of an initiative is RFS?

I might anger some people if I say this, but Mercari’s old business logic prioritized PMF (product-market fit: the degree to which a product satisfies market demand) above anything. Basically, it was built to be used by as many people as possible, as soon as possible. For that reason, while the Mercari service was envisioned to be a five-star hotel, in the end it looked like a roadside inn that just kept tacking on additions.

It is true that this happened naturally alongside the successful way the product and business was led up to this point. But a transformation is essential in order to make things better. If the inn continues the way it handles its customers, we will have more and more illogical issues pop up here and there. My honest feelings are that I’d really rather build a bigger and better inn next door and move there. But we can’t do that. We have to find the compromise between these two ideas and make that a reality. That is what we are doing now in Mercari.

When explaining the difficulty of RFS I often use the metaphor that it’s like trying to change the engine of a plane mid-flight. (laughs)

ーI can only imagine how difficult that can be.

If we can figure this out, we can turn the platform that has been specific to the Mercari business into a third party and a common asset of the Mercari Group. Which means it will be able to support any business Mercari is taking on and will take on in the future. We will be able to add new features faster and accelerate the expansion of the service.

RFS is also about taking better care of our existing systems, because a new feature or a service doesn’t bring in even one yen in profits when it’s first created.

ーIn fact, it’s probably a minus because of the cost attached to building it, right?

That’s right. Operating a feature properly so that it generates money takes a lot of effort, which in turn means it requires money. That’s why we want to improve our current systems in use that are basically “our breadwinners”. I think I would get along with someone who sees value in this sort of action.

There must be people out there who think of this project as simply paying back our tech debt. I don’t like to think of it in this way. I feel that the phrase “tech debt” comes with the nuance that it’s somebody’s fault. But a program has debt from the second it’s launched. Just as it’s nearly impossible to prove bugless code, I think it’s equally difficult to prove a debtless system.

That is why I don’t want to start a fruitless conflict with our past selves and act like our current versions are the heroes. I would much rather have a healthy discussion. A problem that’s currently in question is the low serviceability of our system. The right question to ask is, “How can we fix it?” If we instead asked why it happened or whose fault it is, we wouldn’t be able to resolve a single problem. I say let’s use our time and effort for the solutions.

RFS is the first step to the next Mercari

ーOnce RFS is realized, what phase will Mercari enter?

I’d speak boldly and say it will be Mercari’s second founding. We will be able to launch a new business on top of the foundations built until now. The first step for that is establishing a robust platform. We often talk about how Mercari wants to be a “tech company”. Initiatives like this are a must in order to achieve that vision.

ーIn other words, the big tech companies of the world have already taken care of such problems?

I once had the chance to talk to Mark Zuckerberg. I asked him what he would invest in if he had the funds and opportunity to start over. He immediately responded that he would spend more than half of his resources on the platform as soon as possible.

ーThat’s how important it is to have a strong platform.

In Mercari’s current form, you can witness the technology pushing the business to scale up. This is a rare sight, if I say so myself. Maybe things are not going as rhythmically pleasing as a hop, step, and jump, but you can still witness disruptive growth here.

ーI believe we are currently looking for more people to help us climb this hill. What set of values or outlook would be most fitting for members of this project?

This might be a little bit of a repeat of what I said before, but it’s important that they are able to talk about problems. Among the three processes of solving problems, the role of the engineer is to actually solve the problem. And solve it in an excellent manner, too. Taking the scenic route is a fun expedition on its own, it’s true. But engineering requires the smartest and shortest path to any destination.

Which means it’s very important to understand the core of the problem that you are trying to solve. That is how you achieve excellence. That is the charm and beauty of engineering.

In conclusion

We hope that this article helped you better understand one of the key people leading Robust Foundation for Speed. We are looking for members who can help us achieve the goals of this gigantic project.

If you’re interested, please click the link below to learn more. You will find more technology-focused Mercari Engineering articles written by various project members, as well as information about our hiring events.

We’re looking forward to meeting you! Click here to apply!

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