GATE CS 2024 Set 1 — Question 21

MCQ+1 / -0.33EasyB & B+ TreesTreesProgramming & Data StructuresB+ Tree OperationsIndexing & File OrganizationDatabases

Databases → Indexing & File Organization → B & B+ Trees

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Question

In a B+B^+ tree, the requirement of at least half-full (50%) node occupancy is relaxed for which one of the following cases?
A.
Only the root node
B.
All leaf nodes
C.
All internal nodes
D.
Only the leftmost leaf node

Correct answer

(A) Only the root node

Solution

In a B+B^+ tree of order mm, the standard properties are:
1.Every node except the root must be at least half-full. For an internal node, this means it must have at least m/2\lceil m/2 \rceil children. For a leaf node, it must have at least (m1)/2\lceil (m-1)/2 \rceil keys.
2.The root node is the exception. If it is an internal node, it must have at least 2 children. If it is the only node in the tree (a leaf), it can have as few as 1 key.
Therefore, the 50% occupancy requirement is relaxed only for the root node.

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