The number of sessions specified by the value of the operator MaxSessions attribute are balanced across the number of operator instances. For example, if the Update operator is defined with two instances, and the MaxSessions attribute is set to 4, each instance of the defined Update operator will run two sessions, provided there are at least four AMPs on the system.
An Update operator uses a maximum of one session per available AMP on the database system. This means that if your database system has ten available AMPs, the MaxSessions value must be less than or equal to ten.