The 3.22 version has faster and safer connect code than version 3.21, as well as a lot of new nice enhancements. As there aren't really any major changes, upgrading from 3.21 to 3.22 should be very easy and painless. See 項2.5.4. 「バージョン 3.21 から 3.22 へのアップグレード」.
This is a translation of the MySQL Reference Manual that can be found at dev.mysql.com. The original Reference Manual is in English, and this translation is not necessarily as up to date as the English version.