> You're assuming that you need to change things. Almost all big-data approaches work better when you abandon that and go for a log-structured model where you only ever append.

That depends on your loads. If you're write heavy, then yes. If you're read heavy, then you're adding extra work to find the current row out of all the appends. If you're read and write heavy, then get used to buying really expensive beefy machines and maybe sharding...