The event is market data update. On one hand it is in fact pretty simple. On the other hand, it is not much simpler than something like “user X liked Y” or even “product Z added to cart”. I think it shows what a well designed, optimized code can do on a normal hardware. Remember there is 3-4 billion instructions that a modern cpu is pumping out per second.
One large bank I used to work for had a payment processing system doing about 40 thousand transactions per day. It ran on about $8 million worth of hardware - mainly IBM mainframe. I was impressed until I found out each transaction was essentially a 60-100 byte text message. I can confidently say a well designed system can do 1000 times that load on an iPhone.
Not that it isn't probably still terrible code but the banking system is likely logging the full transaction details every time it is modified / passed to a different part of the system. I.e. fully auditable - if something goes wrong with the transaction it can be fully traced back, corrected and the underlying issue investigated.
