B-Tree Indexes
A b-tree (balanced-tree structured object) index is the default indexing method of Oracle8i. Oracle adapted this indexing method from the start. The index structure resembles a tree in that the top block is read first, then a block in the next layer—which is known as a branch block—is read, and so on, until the index block (known as a leaf block) that contains the actual ROWID is retrieved.
This balancing-structure approach helps minimize I/O. Oracle9i keeps this type of index in order by the assigned key value or values, splitting the blocks if necessary, to keep the structure in sequence. The b-tree structure is stable in that it will take the same number of read operations to retrieve any table row, whatever the size of the ...
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