/// <summary>
/// 分割当前节点
/// </summary>
/// <param name="splitFirstKey">新分割节点的第一个键，也就是最小的键</param>
/// <param name="splitNode">新分割节点</param>
private void SplitInternal(ref string splitFirstKey, ref BPlusTreeNode splitNode)
{
// 从中间开始分割
int splitPoint = this._childNodes.Length / 2 - 1;
// 分割出的新节点的第一个键
splitFirstKey = this._childKeys[splitPoint];
// 新建节点，包含分割点右侧所有数据
splitNode = new BPlusTreeNode(this.Tree, this.Parent, -1, this.IsLeaf);
splitNode.Clear(); // redundant.
// 记录已经扩充的数据结构
long[] values = this._childValues;
string[] keys = this._childKeys;
BPlusTreeNode[] nodes = this._childNodes;
// 重置和清空数据
this.Clear();
// 将分割点左侧的数据拷贝至此节点
Array.Copy(keys, 0, this._childKeys, 0, splitPoint);
Array.Copy(values, 0, this._childValues, 0, splitPoint + 1);
Array.Copy(nodes, 0, this._childNodes, 0, splitPoint + 1);
// 将分割点右侧的数据拷贝至新的分割节点
int remainingKeys = this.Capacity - splitPoint;
Array.Copy(keys, splitPoint + 1, splitNode._childKeys, 0, remainingKeys);
Array.Copy(values, splitPoint + 1, splitNode._childValues, 0, remainingKeys + 1);
Array.Copy(nodes, splitPoint + 1, splitNode._childNodes, 0, remainingKeys + 1);
// 重置新节点中所有的子节点的父节点
splitNode.ResetAllChildrenParent();
// 存储新节点
splitNode.DumpToNewBlock();
splitNode.CheckIfTerminal();
splitNode.Soil();
this.CheckIfTerminal();
}
/// <summary>
/// 合并内部节点，当节点的使用率不足 50% 时，则需要合并
/// </summary>
/// <param name="left">左节点</param>
/// <param name="keyBetween">左右节点的中间键</param>
/// <param name="right">右节点</param>
/// <param name="rightLeastKey">合并后的键的最小值</param>
/// <param name="canDeleteRightNode">是否可以删除右节点</param>
public static void MergeInternal(BPlusTreeNode left, string keyBetween, BPlusTreeNode right, out string rightLeastKey, out bool canDeleteRightNode)
{
if (left == null)
{
throw new ArgumentNullException("left");
}
if (right == null)
{
throw new ArgumentNullException("right");
}
rightLeastKey = null; // only if DeleteRight
// 合并叶节点
if (left.IsLeaf || right.IsLeaf)
{
if (!(left.IsLeaf && right.IsLeaf))
{
throw new BPlusTreeException("Cannot merge leaf with non-leaf.");
}
// 合并子节点
MergeLeaves(left, right, out canDeleteRightNode);
rightLeastKey = right._childKeys[0];
return;
}
// 合并非叶节点
canDeleteRightNode = false;
if (left._childValues[0] == StorageConstants.NullBlockNumber || right._childValues[0] == StorageConstants.NullBlockNumber)
{
throw new BPlusTreeException("Cannot merge empty non-leaf with non-leaf.");
}
string[] allKeys = new string[left.Capacity * 2 + 1];
long[] allValues = new long[left.Capacity * 2 + 2];
BPlusTreeNode[] allNodes = new BPlusTreeNode[left.Capacity * 2 + 2];
// 拷贝左节点的数据
int index = 0;
allValues[0] = left._childValues[0];
allNodes[0] = left._childNodes[0];
for (int i = 0; i < left.Capacity; i++)
{
if (left._childKeys[i] == null)
{
break;
}
allKeys[index] = left._childKeys[i];
allValues[index + 1] = left._childValues[i + 1];
allNodes[index + 1] = left._childNodes[i + 1];
index++;
}
// 拷贝中间键
allKeys[index] = keyBetween;
index++;
// 拷贝右节点的数据
allValues[index] = right._childValues[0];
allNodes[index] = right._childNodes[0];
int rightCount = 0;
for (int i = 0; i < right.Capacity; i++)
{
if (right._childKeys[i] == null)
{
break;
}
allKeys[index] = right._childKeys[i];
allValues[index + 1] = right._childValues[i + 1];
allNodes[index + 1] = right._childNodes[i + 1];
index++;
rightCount++;
}
// 如果数量小于左节点的能力，则右节点可以删除掉
if (index <= left.Capacity)
{
// it will all fit in one node
canDeleteRightNode = true;
for (int i = 0; i < index; i++)
{
left._childKeys[i] = allKeys[i];
left._childValues[i] = allValues[i];
left._childNodes[i] = allNodes[i];
}
left._childValues[index] = allValues[index];
left._childNodes[index] = allNodes[index];
left.ResetAllChildrenParent();
left.Soil();
right.Free();
return;
}
// otherwise split the content between the nodes
left.Clear();
right.Clear();
left.Soil();
right.Soil();
int leftContent = index / 2;
int rightContent = index - leftContent - 1;
rightLeastKey = allKeys[leftContent];
int outputIndex = 0;
for (int i = 0; i < leftContent; i++)
{
left._childKeys[i] = allKeys[outputIndex];
left._childValues[i] = allValues[outputIndex];
left._childNodes[i] = allNodes[outputIndex];
outputIndex++;
}
rightLeastKey = allKeys[outputIndex];
left._childValues[outputIndex] = allValues[outputIndex];
left._childNodes[outputIndex] = allNodes[outputIndex];
outputIndex++;
rightCount = 0;
for (int i = 0; i < rightContent; i++)
{
right._childKeys[i] = allKeys[outputIndex];
right._childValues[i] = allValues[outputIndex];
right._childNodes[i] = allNodes[outputIndex];
outputIndex++;
rightCount++;
}
right._childValues[rightCount] = allValues[outputIndex];
right._childNodes[rightCount] = allNodes[outputIndex];
left.ResetAllChildrenParent();
right.ResetAllChildrenParent();
}