HANA应用了常驻内存、数据源无关的计算引擎，要处理的数据存放在RAM中，而不是从二级存储设备中获取，这样提供了性能的提升。
HANA employs an in-memory, data source agnostic computing engine, where data to be processed is held in RAM instead of reading from secondary storage devices thus providing a performance boost.
说明：如果在查询中使用预先抓取来获取二级缓存中的数据时，我们将无法解决上面提出的问题。
Note: The above issue resolution is not solvable if we are eagerly fetching the second level cached data in our query.
由于磁盘很慢，它从二级缓存中获取数据的速度快于磁盘。
Because disks are slow, it is faster to get data from a level 2 cache than from the disk.
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