Cache the Data Dictionary for Fast Access (264)

Much of the data dictionary information is kept in the SGA in the dictionary cache,
because Oracle constantly accesses the data dictionary during database operation to
validate user access and to verify the state of schema objects. All information is stored
in memory using the least recently used (LRU) algorithm.

Parsing information is typically kept in the caches. The COMMENTS columns describing
the tables and their columns are not cached unless they are accessed frequently.

快取資料字典
1. 大多數的資料字典資訊被快取到SGA中的字典緩衝區 ，使用最近最少使用演算法
2. 解析資訊就是代表性的儲存在快取中

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