innodb_large_prefix
Prefixes, defined by the length attribute, can be up to 767 bytes long for InnoDB tables or 3072
bytes if the innodb_large_prefix option is enabled.
mysql> show variables like 'innodb_large_prefix'
+---------------------+-------+
| Variable_name | Value |
+---------------------+-------+
| innodb_large_prefix | OFF |
+---------------------+-------+
1 row in set (0.00 sec)