[Oracle] Oracle Architecture - SGA

Oracle Database Architecture

※ Create SGA and Administration

1. You connect Oracle server and command 'startup' in Oracle.
2. Then first server process is search a parameter in pfile or spfile.
3. And request to OS kernel. then SGA size is SGA_MAX_SIZE parameter in pfile.
4. OS Kernel is allocate shared memory. On the basis of the value of the semaphore, to manage the SGA.
5. Server process is make instance in shared memory.
6. You can start work in database.

※ What is mean semaphore??

SGA is use shared memory. It is a space in which multiple server processes to use, there is a possibility that multiple processes access to one block. Maybe multiple processes access to one block, it is make problem like kernel panic. So the kernel must be managed to be able to connect only a one process in one block. Kernel to be able to manage such, semaphore is used to display the usage of block.