read _ file函数使用stat函数调用检查文件的修改时间，只有在上一次装载之后修改了文件的情况下，它才重新读取文件的内容。
The read_file function USES the stat function call to check the modification time of the file, only re-reading the contents of the file if it changed since the last time the file was loaded.
需要恢复时，可以读取重新开始区域，并检索最后一次检查点操作中的所有数据。
When a recovery is necessary, you can read a restart area and retrieve all the data from the last checkpoint operation.
则需要对每一次页面装载重新读取数据库，这将在用户数量增加的时候引起麻烦。
This requires a new connection for each page load, which will hurt scalability as the number of users increase.
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