The Alpha 9 is Sony's first 'really' professional mirrorless camera. A novel 24 MP Exmor-RS image sensor with excellent noise performance allows extremely fast continuous shooting (20fps) with no EVF blackout! In addition 4K video, an AF-joystick and all that packed in a rugged body with twice as much battery capacity than the previous A7 cameras.
We generally recommend SDXC memory cards (64GB and more) with an UHS-II-interface and a SD Speed Class from U3/V30 or above, if you're using a Sony A9. Especially during burst shooting, an UHS-II enabled SD card offers a significant advantage in terms of speed.