In this part, I discuss how Oracle uses the machine's memory. Generally, the greater the real memory available to Oracle, the quicker the system runs.
System Global Area (SGA)
The system global area, sometimes known as the shared global area, is for data and control structures in memory that can be shared by all the Oracle background and user processes running on that instance. Each Oracle instance has its own SGA; in fact, the SGA and background processes is what defines an instance. The SGA memory area is allocated when the instance is started, and it's flushed and deallocated when the instance is shut down.
The contents of the SGA are divided into three main areas: the database buffer cache, the shared pool area, and the redo cache. The size of each of these areas is controlled by parameters in the INIT.ORA file. The bigger you can make the SGA and the more of it that can fit into the machine's real memory (as opposed to virtual memory), the quicker your instance will run. Figure 3.4 shows the Oracle SGA in memory.
System Global Area (SGA)
The system global area, sometimes known as the shared global area, is for data and control structures in memory that can be shared by all the Oracle background and user processes running on that instance. Each Oracle instance has its own SGA; in fact, the SGA and background processes is what defines an instance. The SGA memory area is allocated when the instance is started, and it's flushed and deallocated when the instance is shut down.
The contents of the SGA are divided into three main areas: the database buffer cache, the shared pool area, and the redo cache. The size of each of these areas is controlled by parameters in the INIT.ORA file. The bigger you can make the SGA and the more of it that can fit into the machine's real memory (as opposed to virtual memory), the quicker your instance will run. Figure 3.4 shows the Oracle SGA in memory.