SGA_TARGET is a dynamic parameter that can be changed by accessing the SGA Size Advisor from the Memory Parameters SGA page in Oracle Enterprise Manager, or by querying the V$SGA_TARGET_ADVICE view and using the ALTER SYSTEM command. You would set minimum values if an application component needs a minimum amount of memory to function properly. If these automatically tuned memory pools had been set to nonzero values, those values are used as minimum levels by Automatic Shared Memory Management. In response to the workload on the system, the automatic SGA management distributes the memory appropriately for the following memory pools: Set the value of the SGA_TARGET parameter to the amount of memory that you intend to dedicate for the SGA.
To use Automatic Shared Memory Management, set the SGA_TARGET initialization parameter to a nonzero value and set the STATISTICS_LEVEL initialization parameter to TYPICAL or ALL. This section contains the following topics:Īutomatic Shared Memory Management simplifies the configuration of the SGA. For this reason, it is more efficient for data requests of frequently accessed objects to be perform by memory, rather than also requiring disk access.Ī performance goal is to reduce the physical I/O overhead as much as possible, either by making it more likely that the required data is in memory, or by making the process of retrieving the required data more efficient.
Physical I/O also increases the CPU resources required, because of the path length in device drivers and operating system event schedulers. Disk access (physical I/O) take a significant amount of time, compared with memory access, typically in the order of 10 milliseconds.
Memory access is much faster than disk access. Oracle Database stores information in memory caches and on disk. 7.1 Understanding Memory Allocation Issues