以往大部分学者都集中研究磁盘索引，但其实在目前大内存的环境下对内存索引的研究也是非常必要。

For a long time researchers only focus on disk-based index, but research on memory-based index is of great value today because of the mass memory condition.

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请注意，可以根据很多不同的源(例如，RAM磁盘)进行反向索引。

Note that you can back indexing by many different sources, for example, a RAM disk.

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而且，我们希望限制用于建议的索引的磁盘空间。

Also, we want to limit the amount of disk space used for the recommended indexes.

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