这是因为 Oracle 使用大量的虚拟内存，特别是对于其系统全局区域（SGA），这个区域用于缓存表数据和其他东西。

This is because Oracle uses a lot of virtual memory, particularly with respect to its System Global Area (SGA), which is used to cache table data, among other things.

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在第三章中，为了更好的讨论系统的全局拓扑结构，本文首次引入双扇形区域的概念；

In order to achieve a better understanding of global structure of the system, first, we introduce a new concept that is called double sector region in chapter III.

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