I'm trying to migrate from my centos 8 server to an older centos 7 server. migration fails because the key length in one of the mysql databases is too large for the older server mysql (5.5) to handle. (innodb had a key length limitation of 567 in older version). rather than try and fiddle the database keys, it might be easier to upgrade from 5.5 to 5.7 or newer mariadb that CAN handle the longer keys! how can this be done safely?