Oracle 在启动的时候指定SGA使用多少虚拟内存，并且在运行时允许实例通过调整buffer cache， shared pool， large pool和PGA的大小动态的调整SGA。-Oracle boot time designated SGA amount of virtual memory, and at runtime allowing example by adjusting the buffer cache, shared pool, large pool and the size of the PGA dynamic adjustment of SGA.