优化程序采用系统目录，说明那里有多少行，以及构造了较好的索引来计算所采用的查询路径。

The optimizer uses system catalogs indicating how many rows there are and how well the indexes are formed to figure out what query path to use.

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简短地放，一个文件系统是清楚定义的方法计算机的作业系统对商店、目录和取回文件使用。

Briefly put, a file system is a clearly-defined method that the computer's operating system USES to store, catalog, and retrieve files.

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文件系统是一种用来存储和组织计算机文件、目录及其包含的数据的方法，它使文件、目录以及数据的查找和访问得到简化。

A filesystem is a method for storing and organizing computer files and directories and the data they contain, making it easy to find and access them.

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