TheAlgorithms/Go · critical

BTree maxKeys cannot be zero

Error message

BTree maxKeys cannot be zero

What it means

NewBTreeNode panics when maxKeys is <= 0 because a B-tree node needs at least one key slot; the arrays keys and children would be meaningless otherwise. The library treats invalid construction parameters as a programming error, so it panics immediately rather than returning an error.

Source

Thrown at structure/tree/btree.go:26

type BTreeNode[T constraints.Ordered] struct {
	keys     []T
	children []*BTreeNode[T]
	numKeys  int
	isLeaf   bool
}

type BTree[T constraints.Ordered] struct {
	root    *BTreeNode[T]
	maxKeys int
}

func minKeys(maxKeys int) int {
	return (maxKeys - 1) / 2
}

func NewBTreeNode[T constraints.Ordered](maxKeys int, isLeaf bool) *BTreeNode[T] {
	if maxKeys <= 0 {
		panic("BTree maxKeys cannot be zero")
	}
	return &BTreeNode[T]{
		keys:     make([]T, maxKeys),
		children: make([]*BTreeNode[T], maxKeys+1),
		isLeaf:   isLeaf,
	}
}

func NewBTree[T constraints.Ordered](maxKeys int) *BTree[T] {
	if maxKeys <= 2 {
		panic("Must be >= 3 keys")
	}
	return &BTree[T]{
		root:    nil,
		maxKeys: maxKeys,
	}
}

View on GitHub (pinned to 5ba447ec5f)

Solutions

1. Pass a positive maxKeys >= 3 (a B-tree degree parameter) when constructing nodes.
2. Validate any external/config-sourced value before calling NewBTreeNode.
3. Use NewBTree(maxKeys) which enforces maxKeys >= 3 for the top-level entry point.

Example fix

// before
node := NewBTreeNode[int](cfg.MaxKeys, true)
// after
if cfg.MaxKeys < 3 { cfg.MaxKeys = 3 }
node := NewBTreeNode[int](cfg.MaxKeys, true)

func validMaxKeys(n int) bool { return n >= 3 }
if !validMaxKeys(cfg.MaxKeys) { cfg.MaxKeys = 4 }
node := NewBTreeNode[int](cfg.MaxKeys, true)

func safeNewNode[T constraints.Ordered](maxKeys int, leaf bool) (n *BTreeNode[T]) {
    defer func() {
        if r := recover(); r != nil { n = nil }
    }()
    return NewBTreeNode[T](maxKeys, leaf)
}

When it happens

Trigger: Calling NewBTreeNode with maxKeys = 0 or a negative value, e.g. NewBTreeNode[int](0, true), or NewBTree (which calls it via Insert/Split paths) indirectly with a bad size derived from config or user input.

Common situations: Reading maxKeys from a config file or environment variable that is unset (0) or negative; off-by-one or integer division producing 0; copy-pasting a minimal example and passing 0 as a placeholder.

Related errors

• Must be >= 3 keys
• node has too few keys
• node has too many keys
• Called InsertNonFull() with a full node
• deleting out of bounds key

AI-assisted analysis of TheAlgorithms/Go@5ba447ec5f (2026-09-02). Data as JSON: /api/errors/5fbb8bcbf74c984b. Report an issue: GitHub.