Oracle Instance Architecture clearly shows us the combination of background processes and memory structures.
Memory structures consists both SGA and PGA
- SGA – System Global Area is a memory structure which will be allocated in RAM when the Oracle instance is started.
- PGA – Program Global Area is a memory structure which will be allocated in RAM when the server process is started.
The size of the memory structures will be defined in the parameter file or can be mentioned during the installation of database.
Let us first understand the SGA and its internal components.
SYSTEM GLOBAL AREA
As I said earlier that the memory to the SGA is allocated based on values provided during the installation in the initialization parameter file. When the database is started, the first thing it will create is SGA.
SGA consists list of below memory structures.
- Database buffer cache
- Redo Log buffer
- Shared pool (Consists Library cache and Dictionary Cache)
- Java pool
- Streams pool
- Large pool