If your hosting costs are not significant (e.g. you're not a youtube, netflix kind of company where hosting costs eat up a lot of your profits) I think you should optimize for developer productivity instead of computing efficiency. Does it really matter if you spend 20k on hosting instead of 10k if you have to pay your devs 10x that? Just my opinion, curious to hear what other people think

Reducing costs was not the priority during my time there. Fintech startups had a runway that could loop the equator several times - a stark contrast to cash-strapped startups where I did contracts at. It was a real eye opener! It was always a race to get the products out, regardless of cost.

Reminds me of the very first time I went to work for a trading firm. We had been having some performance issues with a particular software system, and so I told the CTO “After looking at all this, if you give us a month I’m pretty sure we can improve performance by about 30%.” He looks at me and then says “Or how about I just get you guys twenty more machines? I can have them here in a couple of days.”

Thats very encouraging to hear. I have been trying to sell our product to enterprise companies and few Fintech companies showed interest, however they are almost 100% Java stack still. In fact I got a big list of concerns/requirements when we said we are based on Node.js - starting with XML processing and distributed transaction.. They cannot imagine using our stack for core business logic because of lack of enterprise features like distributed transaction support. That's when I realized how mature Java is in enterprise adoption compared to other stacks (With .net as an exception.). Wonder if a common standard like JDBC and JMS would help Node.js gain more adoption with enterprises

Somewhere else I saw NodeJS take the lead was parsing of vast quantities of large XML files in the streaming media world.

DDEX is the industry standard for metadata communication (artist, track, licensing, credits, etc.).

One 20-track Xmas classical music compilation album could easily have a single 150MB XML file!

I hypothesise that you’ll find a big variance in backend languages based on when the companies were started.

Companies started 10 years ago tend to have Java / Ruby backends, but companies started in the past 2-3 years will often have NodeJS/Typescript backends.

>and few Fintech companies showed interest

I said Node is dominant in web/APIs, but Fintech I don't expect to go for Node, if we're talking trading, but also for CRUD work.

Fintech doesn’t have anything against node, institutional banking are the ones where old habits die hard.

Is IO the same as requests? i.e. high request demand?

The payment processing was literal parsing of data files on the local disks. It was where modern fintech interfaced with archaic banking technology. Apparently they ran benchmarks and concluded NodeJS was the most suitable for their requirements.

Not necessarily, you could have a few large requests that each do a lot of database work at the backend, that would also be high IO. IO is just any low level network or disk activity that is typically done by the kernel, not the userspace (nodejs) itself.