In case you want to convert your MySQL database tables from utf8 to utf8mb4 please remember that each character will now take 4, not 3 bytes. This means you can

In case you want to convert your MySQL database tables from utf8 to utf8mb4 please remember that each character will now take 4, not 3 bytes. This means you can easily run out of limit for a row length (65536 bytes) if you have many string columns and your indexes will grow. Also, if a column is a part of a foreign key reference you might have to remove the foreign key first, upgrade columns on both sides and add the foreign key back. So converting an existing database might be not as easy as it seems before.