Catalog Information about Indicesfi: average fan-out of internal nodes of index i, for tree-structured indices such as B+-trees.
HTi: number of levels in index i — i.e., the height of i.
For a balanced tree index (such as B+-tree) on attribute A of relation r, HTi = logfi(V(A,r)).
For a hash index, HTi is 1.
LBi: number of lowest-level index blocks in i — i.e, the number of blocks at the leaf level of the index.
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