If you need to purge all the records in the events database of your ZenOSS installation, the simple procedure is the following (tested on Zenoss 2.5.x on Ubuntu server).
# /etc/init.d/zenoss-stack stop
# /etc/init.d/zenoss-stack start mysql
drop the “events” database
# /etc/init.d/zenoss-stack stop mysql
delete the ibdata1 and ib_log* files in the mysql data folder
# /etc/init.d/zenoss-stack start mysql
zenoss$ zeneventbuild localhost [...]