Quiescing mode of database state

Quiesced state
Aim: perform DBA actions (compile objects, alter tables ...)
Conditions:
Active non-DBA sessions go on until they are becoming inactive. No active sessions are allowed to be active, but they will be hung. When the database is unquiesced, all hung sessions are resumed and blocking actions are processed. Issued command will wait  for active sessions to become inactive.
RAC: Quiesce affects all instances.
Command:
ALTER SYSTEM QUIESCE RESTRICTED;
ALTER SYSTEM UNQUIESCE;
Control:
V$BLOCKING_QUIESCE - view where DBA can check the info about sessions that are blocking.