With "sum" functions, I mean that for money transactions the data will likely be stored in columns and the most common operation will likely be to sum each colu

With "sum" functions, I mean that for money transactions the data will likely be stored in columns and the most common operation will likely be to sum each column. So you could store an "archive" with all the columns/transactions, then store just the sum of each column in the "hot" database. If the data is static/immutable you have a lot of options when it comes to caching and optimizing different queries. Another strategy would also be to "shard" the database... I guess storing everything in the same database is the most simple solution, but problems will arise when you have to replicate/recover (an arbitrary) 100+ TB of data. Just copying it over a 100Gbit link will take 3 hours.