1 million. Using as swap with high loads is a very bad idea.
The flash memory may last a few days only. 1 million write / erase cycles is very optimistic, and depends on quality. Cheap USB drive will last 100,000 cycles only. Writing once a sec will eat up 86400 cycles. So the best drive will last 12 days.
Best Regards,
Mukund Deshmukh. Beta Computronics Pvt Ltd 10/1, IT Park, Parsodi, Nagpur-440022 Cell - 9422113746