/// <summary> /// 合并叶子节点,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="right">右节点</param> /// <param name="canDeleteRightNode">是否可以删除右节点</param> public static void MergeLeaves(BPlusTreeNode left, BPlusTreeNode right, out bool canDeleteRightNode) { if (left == null) throw new ArgumentNullException("left"); if (right == null) throw new ArgumentNullException("right"); canDeleteRightNode = false; string[] allKeys = new string[left.Capacity * 2]; long[] allValues = new long[left.Capacity * 2]; int index = 0; for (int i = 0; i < left.Capacity; i++) { if (left.ChildKeys[i] == null) { break; } allKeys[index] = left.ChildKeys[i]; allValues[index] = left.ChildValues[i]; index++; } for (int i = 0; i < right.Capacity; i++) { if (right.ChildKeys[i] == null) { break; } allKeys[index] = right.ChildKeys[i]; allValues[index] = right.ChildValues[i]; index++; } // 如果左节点的容量足够,则可删除右节点 if (index <= left.Capacity) { canDeleteRightNode = true; left.Clear(); for (int i = 0; i < index; i++) { left.ChildKeys[i] = allKeys[i]; left.ChildValues[i] = allValues[i]; } left.Soil(); right.Free(); return; } // 左节点的容量不够了 left.Clear(); right.Clear(); left.Soil(); right.Soil(); int rightContent = index / 2; int leftContent = index - rightContent; int newIndex = 0; for (int i = 0; i < leftContent; i++) { left.ChildKeys[i] = allKeys[newIndex]; left.ChildValues[i] = allValues[newIndex]; newIndex++; } for (int i = 0; i < rightContent; i++) { right.ChildKeys[i] = allKeys[newIndex]; right.ChildValues[i] = allValues[newIndex]; newIndex++; } }
/// <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(); }