Comment by dmd
2 days ago
I'm guessing you've only ever worked at startups?
Large company codebases are very much not like that. I've worked on systems (e.g., banking) that have accreted still-running code for as much as 60 years. Nobody understands how it works. Nobody ever understood how the whole worked, and many of the parts were never actually intended to work together.
This is mostly a self made and kept problem. I also worked in codebases where the current developer(s) didn't know why things were the way they were and would take days to dig into why some part wasn't working - but the issue was, instead of taking the time to write tests and document, even if only when doing these point in time fixes, they just did the ad-hoc thing and solved whatever issue there was at the time without any worry whatsoever.
At some point I was tasked with improving the queries/retrieval times and started converting parts of the code and not only was it possible to write tests that would convey the actual meaning of the code and crystallise it but I started finding bugs in the implementation that no-one realized were even bugs because they no longer knew what it should do when queries grew to certain complexity and the search space was in the hundreds of millions of rows that thinking through them just with napkin calcs wasn't cutting it (specially when the bugs were subtle and the results still allowed the program to work "mostly" correctly).
And this holds true for most of the Internet. There is no one person who truly understands how it all works: DNS, routing, and all the other things we rely on to get our systems to work.
Network engineers and TCP/IP stack implementers have pretty good understanding of how the Internet works.
But I have see quite terrible finance software, patches over patches hold together by a duct tape. Also finance software has to implement large complexity of tax law, which is very large and always changing. It also doesn't help if the company developing finance software sees software development as a cost center and wants always to push the costs down (especially short term costs).
Sure that happens, but over _years_. LLMs can make this happen over _days_.