What is the primary advantage of using a B*-tree over a B-tree for indexing data?

The primary advantage of using a B*-tree over a B-tree for indexing data lies in the way B*-trees handle space utilization.

1. Better Space Utilization: B*-trees guarantee that each internal node (except for the root) is at least 2/3 full instead of half full, as in the case of B-trees. This means that B*-trees make better use of space and require fewer disk accesses.

2. Redistribution during Insertion: When a node in B*-tree is full and we need to insert a new key, B*-trees first try to redistribute keys among the node and its siblings. Only if redistribution is not possible, a split operation is performed. This is different from B-trees, which directly perform a split operation when a node is full. This redistribution in B*-trees leads to a lower height of the tree and hence fewer disk accesses are required.

3. Deletion: During deletion, B*-trees try to merge or redistribute keys to keep the tree balanced and maintain the property that each internal node is at least 2/3 full. This is not the case with B-trees.

In summary, B*-trees are more efficient in terms of space utilization and require fewer disk accesses for operations, which makes them preferable over B-trees for indexing data.