关于Oracle的一本书，英文版的，英文不错的朋友可以看看

The typical cost of using a B-tree index comprises three components—the depth of the index, based on the blevel; the number of index leaf blocks that will be visited, based on leaf_blocks; and the number of visits to table blocks, based on the clust

基于成本的oracle调优(Apress.Cost.Based.Oracle.Fundamentals.Nov.2005.pdf)英文原版