Mediumint is 3 bytes in MySQL. Assuming there are 25000 failed login attempts per day, we will run out of free attempt_id values after

(2^(3×8)÷25000)÷365 = ~2

years.

Solution is to either drop attempt_id if it is not needed or to change it to 4 byte integer.

Considering half a million failed login attempts per day and four bytes:

(2^(4×8)÷500000)÷365 = ~24 years