In redis integer increment commands, more specifically:
INCR / INCRBY
HINCRBY
what is the behavior when incrementing 1-past the maximum value (ie 64bit signed range)?
It would error saying that the increment would overflow:
127.0.0.1:6379> set foo 9223372036854775807
OK
127.0.0.1:6379> incr foo
(error) ERR increment or decrement would overflow