System Architecture 2-141
Structure of an Index Page
Branch Node Pages
The first index branch node is created after the root node and at least two leaf
nodes exist. Regardless of which page fills first, either the root node or one of
the leaf nodes, the result is the creation of a branch node.
If the root node becomes full, it splits and creates two branch nodes, each
with halfof the root node entries. The rootnode retains only three entries: one
pointer to each of the branch nodes and one to the infinity slot.
If one of the leaf nodes becomes full, it splits into two leaf nodes and one
branch node.
Splitting logic is one of the most complicated aspects of index maintenance.
It is not described in detail here. Figure 2-36 illustrates an index with a root
node, two branch nodes, and several leaf nodes.
