UPI: Anatomy of a Payment Transaction

(timeseriesofindia.com)

52 points | by prtk25 5 hours ago ago

16 comments

  • GZGavinZhao 16 minutes ago ago

    How is this different from Alipay/WeChat Pay in China? Handling transactions of this volume is an amazing technological feat, kudos to the team! However, I don't think this mobile QR code paying system is anything novel. Alipay rose to popularity much earlier (I can't recall exact when, but it was already super popular in ~2010, and definitely ubiquitous by 2015).

    • repeekad 3 minutes ago ago

      Much of the world doesn’t like having a single entity own and control the process end to end, it’s more efficient but there’s only one point of trust. Multiple institutions that have to check each other means you don’t have to trust a single entity with everything.

  • elendilm 34 minutes ago ago

    I have the utmost respect to people who makes UPI work. Made even the old people in the nation completely go digital for payments - a feat unparalleled in the world.

  • pzmarzly 3 hours ago ago

    22B transactions a year mean an average of ~700 QPS for the NPCI switch. Of course the traffic is not uniform, it probably peaks at many times that number, but that still doesn't sound that bad - for comparison, a quick Google tells me Nasdaq TotalView ITCH feed peaks at 100k+ QPS at market open.

    • vinay_ys an hour ago ago

      The right comparison for Nasdaq's order processing volume or messaging volume would be India's National Stock Exchange (NSE). It does more executed orders per day than nasdaq.

      I worked on scaling UPI a few years ago. Real-time Payments is vastly more complex as it is much more distributed - each transaction involves the two banks holding funds, two end-user apps (and their banks), and the network (npci) – for the payment to complete end to end, multiple message exchanges need to happen between these parties while the user at both ends are waiting. So, if you measure the scale in messages/sec it would 10-25x higher.

      Real-time payment rails that works 24/7 365 days a year from any bank to any bank (domestic, no exceptions) for free is truly a game-changer. Compare that to US payment rails which is slow and expensive. Apart from UPI, India has 3 more payment rails – NEFT (similar to ACH – batch settlement), IMPS (similar to UPI, instantaneous - but different user experience), RTGS (real-time, intermediated by the central bank RBI, but only for high-value transactions) – all are 24/7/365 and free. Then, there's credit card rails – apart from Visa and Mastercard, India also has RuPay which has much lower interchange rate.

    • repeek 3 hours ago ago

      22B in the month of June 2026, so 264B extrapolated annually.

    • arter45 an hour ago ago

      A great lesson for system design job interviews - if this is a popular payment system in a country with 1.5 billion people, your theoretical system you're designing for a small company cargo culting Google interviews will not likely support millions or even tens of thousands of average TPS.

  • jesuswasjew 2 hours ago ago

    Centralized, kyced, private money transaction network. Is this something good?

    • pixelatedindex 39 minutes ago ago

      It’s extremely good, at least in terms of user experience and how practical it is. Adoption is massive and at small chai shops it makes transactions a breeze, allowing businesses to serve more volume. The downside is making it incredibly frustrating for foreigners to pay using this as it’s tied to your government ID that your bank has authorized.

    • haskman 2 hours ago ago

      Yes it is. It's not trying to be new money, it's your money that already works.

    • ChrisMarshallNY an hour ago ago

      I have heard nothing but good about it, from my Indian friends. They rave about it.

    • toomuchtodo an hour ago ago

      Yes, it is peak developed world financial infrastructure, ran as a utility under government direction.

    • fragmede 2 hours ago ago

      How is it KYCd yet also private?

      • globemaster99 37 minutes ago ago

        It's the intention and use case. The government want to reduce the fund leakages and reduce corruption, directly transfer the money to citizens, reduce transaction costs. Hence it works.

        The government does not track all the transactions. You need a police FIR, to review these transactions.

        In short, Indian government does not track or they don't have the scaling to track. But they can do it, if there is any criminal complaint.