TheAlgorithms/Go · error

node has too many keys

Error message

node has too many keys

What it means

Verify panics when a node holds more keys than the tree's maxKeys, exceeding the node's allocated capacity. Normally splits in Insert keep nodes within capacity, so this signals an out-of-band mutation or a node shared between trees with different maxKeys.

Source

Thrown at structure/tree/btree.go:50

	}
}

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

func (node *BTreeNode[T]) Verify(tree *BTree[T]) {
	minKeys := minKeys(tree.maxKeys)
	if node != tree.root && node.numKeys < minKeys {
		panic("node has too few keys")
	} else if node.numKeys > tree.maxKeys {
		panic("node has too many keys")
	}
}

func (node *BTreeNode[T]) IsFull(maxKeys int) bool {
	return node.numKeys == maxKeys
}

func (node *BTreeNode[T]) Search(key T) bool {
	i := 0
	for ; i < node.numKeys; i++ {
		if key == node.keys[i] {
			return true
		}
		if key < node.keys[i] {
			break
		}
	}
	if node.isLeaf {

View on GitHub (pinned to 5ba447ec5f)

Solutions

1. Only insert keys through tree.Insert, which triggers Split when nodes fill.
2. Keep node ownership 1:1 with a single BTree and its maxKeys.
3. Rebuild the tree from scratch (re-insert all keys) if nodes were transferred between trees.
4. Run root.Verify after manual manipulations to catch corruption early.

Example fix

// before
leaf.Append(k, nil) // can exceed maxKeys
// after
tree.Insert(k) // splits full nodes automatically

if tree.root != nil {
    tree.root.Verify(tree) // panics if any node overflows
}
tree.Insert(key)

func safeInsert[T constraints.Ordered](t *BTree[T], k T) {
    defer func() { _ = recover() }()
    t.Insert(k)
}

When it happens

Trigger: Inserting into nodes without going through the tree's split logic (calling node-level helpers directly); moving a node from a tree with larger maxKeys into a tree with smaller maxKeys and calling Verify; writing past numKeys accounting with direct key appends.

Common situations: Copying nodes between BTree instances in tests or serialization code; custom batch-insert code that bypasses InsertNonFull's split path.

Related errors

• node has too few keys
• nodes should not have less than the minimum number of keys
• cannot delete key from node with minimum number of keys
• BTree maxKeys cannot be zero
• Must be >= 3 keys

AI-assisted analysis of TheAlgorithms/Go@5ba447ec5f (2026-09-02). Data as JSON: /api/errors/4d3ce4398a39405b. Report an issue: GitHub.