Comment # 9 on bug 1217688 from Jiri Slaby

In mysql:
> mysql> ALTER TABLE sources CHANGE COLUMN src src VARCHAR(769) NOT NULL UNIQUE;
> ERROR 1071 (42000): Specified key was too long; max key length is 3072 bytes

The maximum length of UNIQUE column in mysql is 3072 bytes, i.e. 768 utf8mb4
chars.

So if I do this in mariadb:
> MariaDB [structs_66]> ALTER TABLE sources CHANGE COLUMN src src VARCHAR(768) NOT NULL UNIQUE;
everything works. If I enlarge to 769, it breaks:
> MariaDB [structs_66]> ALTER TABLE sources CHANGE COLUMN src src VARCHAR(769) NOT NULL UNIQUE;