Meet Santanu Sinha, Architect behind PhonePe’s central processing system

Santanu loves scale! The whizz architect builds systems that can handle tens of thousands of requests per second. At PhonePe, he has built the central transaction processing system – and this is not his first rodeo! Having contributed to ebooks systems and the event storage platform (Foxtrot) at Flipkart, he’s also credited with building the (now open source) Fabric stream processing engine on Mesos/Marathon at OLA. Let’s hear more from the man himself…

What are the functions you own at PhonePe?

I’m responsible for the core user interaction and payments related systems, and the infrastructure level services used by other teams. That could extend to quite a few things – like global system scalability, system audits and security and fraud detection.

The most exciting project you’ve worked on till date…

That would be the motherlode –  the central transaction processing system at PhonePe. It easily handles millions of transactions every day, and can handle millions more. At heart, it remains the core system we began with, proving that we made the right architecture, stack and design choices at that time.

The one aspect of the job that drives you the most…

The level of impact we can create in a user’s life is the primary driver for all of us here. For instance, we are enabling instant money transfer from bank to bank using UPI, that has made life easier for a lot of people. Also, PhonePe is a delightful place to work for people who are intrigued by scalable systems. The problems we solve here are complex and focussed engineering is required to solve them.

What’s your personal work style?

I work in a fast iterative mode, starting off with basic architecture and design based on the requirements of the stakeholder teams. Afterwards, it’s a cycle of small iterations building up to the end result. With my team, I take a hands-off approach and help people grasp the fundamentals as a part of the journey. Discussions never get to the point where I’m telling someone a ‘How’, it’s always about them arriving at the right conclusion.

How do you decide on incorporating new tech?

Given the deep reliance of our users on PhonePe, we always favour stability and scalability over novelty. There are several areas like ML where we are using fairly bleeding edge stuff. All our tech stack is based on open source components and we do make necessary changes and publish patches upstream.Your favourite bit about working at PhonePe…

Cliche as it sounds – the culture! We have a merit-based culture, and not just on paper. Nothing is taken at face value and everything is reviewed and debated – irrespective of the participants. Our hierarchy and processes are geared towards upholding it and every one is signed on to maintain it.

The values your team swears by…

Integrity, customer focus, an extremely paranoid view on data security, thinking about scalability in every small piece of code, equality in the workplace, and a general sense of everyone being a part of the same journey.

If you could give one piece of advice to young techies…

Focus on the fundamentals, ye young ones! Jazzy frameworks will come and go. The fundamentals will stick with you, so will good design. Think about performance and scalability in everything you do. You never know when your three-person garage startup will become big and there will be millions of bumps along the road. Having sound software will smooth out a few of them!