[mrcarruthers]

And here's the commit that changed it: https://github.com/mysql/mysql-server/commit/43a506c0ced0e6e.... It was originally set to max 6 bytes but for some reason someone dropped it to 3.

They also seem to be slowly phasing it out. Internally it's utf8mb3 and utf8 is just an alias. The idea is to eventually make utf8 an alias to utf8mb4.

[isotopp]

Back then MySQL used the memory engine for implicit temporary tables, and memory engine has no variable width data types. So a "varchar" becomes a "char", and a "varchar(255) charset utf8" becomes an allocation of six times 255 = 1530 bytes (filled with a lot of padding).

Reducing this to 3 bytes is still bad, but only half as bad as before.

Only MySQL 8 introduced innodb typed temporary tables (unlogged, even), so with MySQL 8 this is no longer a problem.