To perform several jobs in Oracle 12C Memory Architecture, the database will create and use memory structures. For instance, The data that is shared among the clients will be executed in the store programs inside the memory.
An System global area and Oracle processes constitute an Oracle instance. Oracle 12C Memory Architecture automatically allocates memory for an System global area while starting of an instance, and the operating system reclaims the memory when you shut down the instance. Each instance has its own SGA.
The System global area will write/read. All the read information contained within the instances of system global area, will be connected to multi-process database instance and several processes write to the SGA during execution of Oracle. The data structures contained in the system global area are:
The life of the session, the user global area must be available to a database session.Due to this reason, When using a shared server connection the user global area cannot be stored in the program global area because a single process is specific to the program global area. Therefore, when using shared server connections the user global area is stored in the system global area, enabling any shared server process access to it. When using a dedicated server connection, the user global area stored in system global area.
Oracle 12C Database supports different memory administration strategies, which are picked by instatement parameter settings. Oracle suggest to enable the technique known as automatic memory management.