/// <summary>
/// 删除指定的键和关联的数据项。如果键未找到则抛出异常。
/// </summary>
/// <param name="key">被删除的键</param>
public void RemoveKey(string key)
{
if (this.RootNode == null)
{
throw new BPlusTreeKeyNotFoundException("Tree is empty, cannot remove.");
}
bool mergeMe;
BPlusTreeNode root = this.RootNode;
// 从根节点开始遍历删除
root.Delete(key, out mergeMe);
// 如果根节点不是一个叶节点，并且仅还有一个子节点，则重新设置根节点
if (mergeMe && !this.RootNode.IsLeaf && this.RootNode.Count == 0)
{
this.RootNode = this.RootNode.FirstChild();
this.RootNodeBlockNumber = this.RootNode.MakeAsRoot();
root.Free();
}
}
/// <summary>
/// 删除指定键的记录
/// </summary>
/// <param name="key">指定键</param>
/// <param name="mergeMe">如果为真则意味着删除键后节点已经小于1/2满，需要合并</param>
/// <returns>返回节点中最小的键，如无变化则返回空</returns>
public string Delete(string key, out bool mergeMe)
{
// 如果是叶节点，则调用删除叶节点逻辑
if (this.IsLeaf)
{
return(DeleteLeaf(key, out mergeMe));
}
// 假设我是不需要被合并的
mergeMe = false;
// 我是内部节点，找到指定键的位置
int deletePosition = this.FindAtOrNextPosition(key, false);
// 加载要被删除位置的子节点
BPlusTreeNode deleteChildNode = LoadNodeAtPosition(deletePosition);
// 从子节点中删除键
bool isChildNodeNeedMerge;
string deletedChildKey = deleteChildNode.Delete(key, out isChildNodeNeedMerge);
// 删除完毕，当前节点为脏节点
this.Soil();
// 发现子节点的最小键与被删除的键相同，则认为子节点已经没用了
string result = null;
if (deletedChildKey != null && this.Tree.CompareKey(deletedChildKey, key) == 0)
{
if (this.Capacity > 3)
{
throw new BPlusTreeException(
string.Format("Deletion returned delete key for too large node size: {0}.",
this.Capacity));
}
// 判断删除的是头或尾
if (deletePosition == 0)
{
result = this._childKeys[deletePosition];
}
else if (deletePosition == this.Capacity)
{
this._childKeys[deletePosition - 1] = null;
}
else
{
this._childKeys[deletePosition - 1] = this._childKeys[deletePosition];
}
if (result != null && this.Tree.CompareKey(result, key) == 0)
{
this.LoadNodeAtPosition(1);
result = this._childNodes[1].LeastKey();
}
// 这个子节点彻底没用了，释放其空间
deleteChildNode.Free();
// 节点中键位置右侧全部左移 1 位
OverwriteDeletePosition(deletePosition);
// 如果节点的使用率小于一半，则需要合并节点
if (this.Count < this.Capacity / 2)
{
mergeMe = true;
}
// 重置子节点的父节点
this.ResetAllChildrenParent();
return(result);
}
if (deletePosition == 0)
{
result = deletedChildKey;
}
else if (deletedChildKey != null && deletePosition > 0)
{
if (this.Tree.CompareKey(deletedChildKey, key) != 0)
{
this._childKeys[deletePosition - 1] = deletedChildKey;
}
}
// 如果子节点需要合并
if (isChildNodeNeedMerge)
{
int leftIndex, rightIndex;
BPlusTreeNode leftNode, rightNode;
string keyBetween;
if (deletePosition == 0)
{
// 和右侧兄弟节点合并
leftIndex = deletePosition;
rightIndex = deletePosition + 1;
leftNode = deleteChildNode;
rightNode = this.LoadNodeAtPosition(rightIndex);
}
else
{
// 和左侧兄弟节点合并
leftIndex = deletePosition - 1;
rightIndex = deletePosition;
leftNode = this.LoadNodeAtPosition(leftIndex);
rightNode = deleteChildNode;
}
keyBetween = this._childKeys[leftIndex];
// 合并节点
string rightLeastKey;
bool isDeleteRight;
MergeInternal(leftNode, keyBetween, rightNode, out rightLeastKey, out isDeleteRight);
// 是否需要删除右节点
if (isDeleteRight)
{
for (int i = rightIndex; i < this.Capacity; i++)
{
this._childKeys[i - 1] = this._childKeys[i];
this._childValues[i] = this._childValues[i + 1];
this._childNodes[i] = this._childNodes[i + 1];
}
this._childKeys[this.Capacity - 1] = null;
this._childValues[this.Capacity] = StorageConstants.NullBlockNumber;
this._childNodes[this.Capacity] = null;
this.ResetAllChildrenParent();
rightNode.Free();
// 当前节点还需要再合并吗
if (this.Count < this.Capacity / 2)
{
mergeMe = true;
}
}
else
{
this._childKeys[rightIndex - 1] = rightLeastKey;
}
}
return(result);
}
public string Delete(string key, out bool mergeMe)
{
if (this.IsLeaf)
{
return(DeleteLeaf(key, out mergeMe));
}
mergeMe = false;
int deletePosition = this.FindAtOrNextPosition(key, false);
BPlusTreeNode deleteChildNode = LoadNodeAtPosition(deletePosition);
bool isChildNodeNeedMerge;
string deletedChildKey = deleteChildNode.Delete(key, out isChildNodeNeedMerge);
this.Soil();
string result = null;
if (deletedChildKey != null && this.Tree.CompareKey(deletedChildKey, key) == 0)
{
if (this.Capacity > 3)
{
throw new BPlusTreeException(
string.Format("Deletion returned delete key for too large node size: {0}.",
this.Capacity));
}
if (deletePosition == 0)
{
result = this._childKeys[deletePosition];
}
else if (deletePosition == this.Capacity)
{
this._childKeys[deletePosition - 1] = null;
}
else
{
this._childKeys[deletePosition - 1] = this._childKeys[deletePosition];
}
if (result != null && this.Tree.CompareKey(result, key) == 0)
{
this.LoadNodeAtPosition(1);
result = this._childNodes[1].LeastKey();
}
deleteChildNode.Free();
OverwriteDeletePosition(deletePosition);
if (this.Count < this.Capacity / 2)
{
mergeMe = true;
}
this.ResetAllChildrenParent();
return(result);
}
if (deletePosition == 0)
{
result = deletedChildKey;
}
else if (deletedChildKey != null && deletePosition > 0)
{
if (this.Tree.CompareKey(deletedChildKey, key) != 0)
{
this._childKeys[deletePosition - 1] = deletedChildKey;
}
}
if (isChildNodeNeedMerge)
{
int leftIndex, rightIndex;
BPlusTreeNode leftNode, rightNode;
string keyBetween;
if (deletePosition == 0)
{
leftIndex = deletePosition;
rightIndex = deletePosition + 1;
leftNode = deleteChildNode;
rightNode = this.LoadNodeAtPosition(rightIndex);
}
else
{
leftIndex = deletePosition - 1;
rightIndex = deletePosition;
leftNode = this.LoadNodeAtPosition(leftIndex);
rightNode = deleteChildNode;
}
keyBetween = this._childKeys[leftIndex];
string rightLeastKey;
bool isDeleteRight;
MergeInternal(leftNode, keyBetween, rightNode, out rightLeastKey, out isDeleteRight);
if (isDeleteRight)
{
for (int i = rightIndex; i < this.Capacity; i++)
{
this._childKeys[i - 1] = this._childKeys[i];
this._childValues[i] = this._childValues[i + 1];
this._childNodes[i] = this._childNodes[i + 1];
}
this._childKeys[this.Capacity - 1] = null;
this._childValues[this.Capacity] = StorageConstants.NullBlockNumber;
this._childNodes[this.Capacity] = null;
this.ResetAllChildrenParent();
rightNode.Free();
if (this.Count < this.Capacity / 2)
{
mergeMe = true;
}
}
else
{
this._childKeys[rightIndex - 1] = rightLeastKey;
}
}
return(result);
}
