a) Big data is more than just the size of the data. It's about how you treat that data i.e. instead of doing expensive and brittle up-front RDBMS modelling you instead dump it all into a data lake and figure out how to handle the data at run-time. And it is still the standard pattern in almost all companies today.

b) Nobody was choosing MongoDB solely for performance. If it was you would choose some in-memory K/V store. It was about it being the only well supported document store that was also fast and scalable.

c) Stripe’s DocDB is an extension of MongoDB Community: https://stripe.com/blog/how-stripes-document-databases-suppo...