As a former Adyen employee, I can confirm that they use the relational features a lot. It's a ledger with millions (probably billions by now) of financial recor

As a former Adyen employee, I can confirm that they use the relational features a lot. It's a ledger with millions (probably billions by now) of financial records, and it's heavily optimized for flexible querying. You have raw tables of transactions that are linked to many other tables (accounts, exchange rates, risk, transaction accept/capture/settle records, batches etc.), and you can ideally query the state of any transaction by just joining those tables on the db. What they also have is plenty of aggregate tables materialized by consumers and compactors, which are used a lot for reporting and auditing - for instance, daily transacted amount broken down by account and currency, or monthly revenue reports broken down by marketplace and currency. Additionally, being a financial institution they are also compelled to hold these records for several years, so there aren't many options for reducing the size of the db by aggregating/moving old records.