Database Index Trees
Databases operate primarily on storage systems where disk or SSD I/O is far more expensive than an in-memory pointer operation. B-Trees and B+ Trees have high branching factors, which make the tree shallow and reduce the number of pages that must be read. B+ Trees also place records or record pointers in leaves and link the leaves, making range scans efficient.
High fan-out reduces tree height.
Nodes are designed around storage pages or blocks.
Fewer levels mean fewer I/O operations.
B+ Tree leaves support efficient sequential and range scans.
Database indexes need predictable performance at large scale.