VAST systems leverage deep write buffers built from low-cost persistent memory, this allows for every ACID transaction to be stored instantaneously.
As tables fill, they are then migrated down to low-cost hyperscale flash and stored in a columnar format, so that queries also run instantaneously.
Queries cut across both the long-term datastore and the write buffer, and even though data accessed in the buffer is row-based, the underlying persistent memory structures make any row reads lightning fast.