In order to decrease the layer of tree, consequently decrease the cost of disk I/O, the index structure in traditional DRDBs (Data Resident Databases) is usually B-tree or the variables of B-tree.

• 在传统的磁盘数据库中采用的索引结构通常是B树或B树的变种，其目的是减少树的层次，从而减少磁盘I/O的开销。