I realise I live in a strange world when my first thought reading this is "Worldwide? That’s low. Fits in the basic one region, one account concurrent AWS Lambda quota. No need to even ask support for the 10k."
> How many times do you buy things during a day? Once? twice? Maybe thrice?
None most days. But then some days eight or nine subscriptions go through. Guess it averages out.
Might be spiky though, around the beginning and ends of each month. If paying out wages monthly, and at the end of the month or beginning of the next one is prevalent across countries where a significant share of the population has both access to a bank account and sufficient enough income to regularly spend either by card or online.
Did this turn into a systems design interview?
Anyway, joking aside, I was mostly amused by what my frame of reference for throughput / service load has become.
And let me state again, if you're a payments processor and you're processing 500-1000 payments PER SECOND on average, that makes you a very big company indeed (multi billion dollar company).
You can do the math, work out how many payments that is, what an average value of payment is, and what the TPV would be for a month. You can easily run into huge numbers that way.
And don't forget, the payment processors are taking percentages in most cases, so that 120 payments per second can turn into a huge amount of revenue at the end of the month.