At previous job, in an an human ads evaluation team, we had a big row table that got turned into column oriented one every couple of hours. I think it got close

At previous job, in an an human ads evaluation team, we had a big row table that got turned into column oriented one every couple of hours. I think it got close to million columns (expanded from leaf protobuf fields). We had some black/white listing as the schema grew too big (~20GB? just the schema, and the limits were few gigs). That was years ago, so probably changed a lot. But the use case was for various analysts (statisticians, linguists, etc., or any internal users other teams of the table). As their quires might use any column they like - there was probably a way to track down which columns got used over a time, but since it was used for launching new things, you would not know - better be safe than sorry I guess. Anyway, I'm still fascinated that this terabyte thing got converted using 20k machines for few hours and worked! (it wasn't streaming, it was converting over and over from the begining, this might've changed too!)