Sunday, April 15, 2012

Oracle Instance

When Oracle starts up in UNIX, the processes are of many names and they are referred as Oracle background processes.  They are persistent and exist from the time when Oracle is started until it is shut down.  They are started from a single Oracle executable but they picked up different personalities depending on the functions they perform. In Windows, these processes becomes individual thread in a single process.

Oracle SGA is a shared memory segment that are attached to by the background processes.  In UNIX, the processes uses shmget() and shmat() calls. Under Windows, the threads use C call malloc() to allocate the memory and share it within one address space.

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