/// <summary>
/// 在节点中插入键值对
/// </summary>
/// <param name="key">叶子节点的键</param>
/// <param name="value">键对应的值</param>
/// <param name="splitFirstKey">if not null then the smallest key in the new split leaf</param>
/// <param name="splitNode">if not null then the node was split and this is the leaf to the right.</param>
/// <returns>
/// null unless the smallest key under this node has changed, in which case it returns the smallest key.
/// </returns>
public string Insert(string key, long value, out string splitFirstKey, out BPlusTreeNode splitNode)
{
if (this.IsLeaf)
{
return this.InsertLeaf(key, value, out splitFirstKey, out splitNode);
}
// 我不是叶子 我是中间节点 找到Key对应的位置 在子节点中插入键值对
splitFirstKey = null;
splitNode = null;
// 查找新键的位置 由于是中间节点 则新键的位置必须存在
int insertPosition = this.FindAtOrNextPosition(key, false);
// 非叶子节点中的值数组存储叶子节点的块序号
long insertValue = this.ChildValues[insertPosition];
if (insertValue == StoredConstants.NullBlockNumber)
{
throw new BPlusTreeException("key not followed by block number in non-leaf");
}
// 加载子节点
BPlusTreeNode insertChild = this.LoadNodeAtIndex(insertPosition);
string childSplitFirstKey;
BPlusTreeNode childSplitNode;
// 在子节点中插入新的键值对
string childInsert = insertChild.Insert(key, value, out childSplitFirstKey, out childSplitNode);
// 发现子节点已满，也需要分割
if (childSplitNode != null)
{
// 我即将被更改
this.Soil(); // redundant -- a child will have a change so this node will need to be copied
// 为新的子节点创建位置索引，即下一个
int newChildPosition = insertPosition + 1;
// 自己是否已满
bool doSplit = false;
// 如果我作为中间节点容量也满了，则中间节点也需要被分割
if (this.ChildValues[this.Capacity] != StoredConstants.NullBlockNumber)
{
doSplit = true;
}
if (doSplit)
{
// 做分割准备
this.PrepareBeforeSplit();
}
// bubble over the current values to make space for new child
// 新节点位置上及其右侧内容全部向右移动1位，为新节点空出位置
for (int i = this.ChildKeys.Length - 2; i >= newChildPosition - 1; i--)
{
int iPlus1 = i + 1;
int iPlus2 = iPlus1 + 1;
this.ChildKeys[iPlus1] = this.ChildKeys[i];
this.ChildValues[iPlus2] = this.ChildValues[iPlus1];
this.ChildNodes[iPlus2] = this.ChildNodes[iPlus1];
}
// record the new child
// 新节点的位置存放新节点的第一个键
this.ChildKeys[newChildPosition - 1] = childSplitFirstKey;
// 被分割出的子节点的父节点为自己
childSplitNode.ResetParent(this, newChildPosition);
// 如果我作为中间节点容量也满了，则中间节点也需要被分割
if (doSplit)
{
// 从中间开始分割 折半
int splitPoint = this.ChildNodes.Length / 2 - 1;
// 分割出的新节点的第一个Key
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();
} // end do split
// 重置节点中所有的子节点的父节点
this.ResetAllChildrenParent();
}
// 返回最小的那个键
if (insertPosition == 0)
{
return childInsert; // the smallest key may have changed
}
else
{
return null; // no change in smallest key
}
}
/// <summary>
/// 合并节点，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 Merge(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
// 合并叶子节点
if (left.IsLeaf || right.IsLeaf)
{
if (!(left.IsLeaf && right.IsLeaf))
{
throw new BPlusTreeException("can't merge leaf with non-leaf");
}
// 合并子节点
MergeLeaves(left, right, out canDeleteRightNode);
rightLeastKey = right.ChildKeys[0];
return;
}
// 合并非叶子节点
canDeleteRightNode = false;
if (left.ChildValues[0] == StoredConstants.NullBlockNumber || right.ChildValues[0] == StoredConstants.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();
}