I read that one way to switch the load plan is through scheduler. I guess scheduler will switch to a plan by taking switching decision based on time. It will not take switching decision based on need and availability of resources among various consumer user groups?

Let's say 90% of resource is guaranteed to processing user group (a group of OLTP users) and 10% resource to reporting user group, however processing user group is able to utilize only 80%. In this situation a new session/call or existing session/call from reporting user group will be automatically switched to processing user group?

or sessions/calls will not switch , however resources will be allocated to processing user group?

How DBRM knows (or how to implement that if processing user group needs only 80% at the moment (whilst guarantee is set to 90%) then remaining 10% should be allocated to other needy reporting user group?

However in next moment again needs change and now processing user group needs more then resource consumption will be automatically switched to 90% to processing user group and 10% to reporting user group?

If it happens and in automatically fashion then this switching may cause additional overhead? I mean DBRM is busy most of the time in switching and actual task is not being performed?

SQL> select name from v$event_name
  2  where name like '%res%mgr%';

NAME
--------------------------------------
resmgr: redo throttle
resmgr:cpu quantum
resmgr:large I/O queued
resmgr: I/O rate limit
resmgr:internal state change
resmgr:sessions to exit
resmgr:become active
resmgr:pq queued
resmgr:plan change
resmgr:internal state cleanup