Slideshow:

Structure of a leaf node

The index file are stored in the leaf nodes

Each leaf node store a number of search keys and their record addresses to the data file

The last pointer in a leaf node

We can traverse the index file in search key order using the last pointer in the leaf nodes

Occupancy constraint of an leaf node

Occupancy constraint of an internal node

Summary+examples: structure and occupancy constraints on internal node

Summary: occupancy constraints

❮ ❯

Structure of a leaf node of a B⁺-tree

Structure of an leaf node :

Explanation:

Each leaf node of the B⁺-tree is also stored inside 1 disk block
Search keys in a node are the search values that you want to use to speed up the search operation
The pointers in the leaf node (except the last pointer) are database addresses (= pointers) to blocks that contains the record with the corresponding search key
The "last" pointer in a leaf node of a B⁺-tree:

Note:

The leaf nodes of the B⁺-tree contains (= are) the index file !!!

Occupancy constraint of an leaf node of a B⁺-tree

Occupancy constraint on an leaf node:

At least half of the search keys (and corresponding record pointers) in an leaf node must be used

Example:

Suppose that a leaf node can store:

n search keys
n block pointers (= database addresses) to data blocks
The last pointer points to the next leaf node (= a disk block !) in the B⁺-tree

A full leaf node is as follows:

Each leaf node (except when the leaf node is the root node) must have ≥ ⌈ n/2 ⌉ keys
A minimal leaf node looks like this:

Summary on leaf nodes
Summary: all structural requirements of a B⁺-tree
- The following figure summarizes the structural requirement of a B⁺-tree:
- Content of an internal node:
- Content of an leaf node: