Comment by whstl

That was the reality of the fintech I worked at.

The schema wasn't really a problem, but the sheer amount of queries per request. Often a user opening a page or clicking a button would cause 100-200 database queries, including updates. This would prevent strategies such as "just replicating the data somewhere". It was so badly architected that every morning the app would stop responding due to users doing their morning routine operations. And they only had around 300 employees.

And this was just an internal app, the B2C part was already isolated because we couldn't afford to be offline.

The solution I started working on was doing similar to the strangler fig pattern and replacing parts of the API with new code that talked directly to the ORM. Naturally this didn't made the people who wrote the legacy code happy, but at least the outages stopped.