Online truncation of InnoDB undo tablespaces

A new feature that's in mysql 5.7, which is very useful. Especially when we have Galera Cluster enabled, as Galera will copy all files included the undo log tablespaces to a new node. If we can do this house keeping job for the server, we can utilize disk space in a much better way, and have a new node setup much faster.

https://dev.mysql.com/doc/refman/5.7/en/truncate-undo-tablespace.html
http://mysqlserverteam.com/online-truncate-of-innodb-undo-tablespaces/