PZnn Processes!!!

Dont know dont ask but these PZ99 and PZ98 processes contributed in loosing my hair!!!
Never heard of them before and ever cared to see what those are untill I recently found that the little tool that I wrote to kill all the sessions in the database was failing in RAC databases (you can find that in my earlier posts).

This little tool was suppose to go and kill all the sessions that are connected in the database prior to doing any upgrades and they started failing.
When I looked at there are these processes PZ99 and PZ98 sitting in gv$session and thier serial# keeps changing everytime you run a query against gv$session view and thus my little killing a session in RAC fails as the serial# is changed!!!

Anyways, what are these PZnn processes?
These are PQ slaves used for global views that are RAC Parallel Server Slave processes, but they are not normal parallel slave processes, PZnn processes (starting at 99) are used to query GV$ views which is done using Parallel Execution on all instances, if more than one PZ process is needed, then PZ98, PZ97,... (in that order) are created automatically.