/// <summary>
/// 构造B+树存储头
/// </summary>
/// <returns></returns>
private byte[] MakeHeader()
{
// 魔数前缀 | 版本 | 节点容量 | 键大小 | 根节点块序号 | 空闲块头序号
// prefix | version | node size | key size | block number of root | block number of free list head
byte[] header = new byte[HeaderSize];
// 魔数前缀
StoredConstants.TreeFileHeaderPrefix.CopyTo(header, 0);
// 版本 1 Byte
header[StoredConstants.TreeFileHeaderPrefix.Length] = Version;
// 节点容量 4 Bytes
int index = StoredConstants.TreeFileHeaderPrefix.Length + 1;
StoredHelper.Store(this.NodeCapacity, header, index);
index += StoredConstants.IntegerLength;
// 键大小 4 Bytes
StoredHelper.Store(this.KeyLength, header, index);
index += StoredConstants.IntegerLength;
// 根节点块序号 8 Bytes
StoredHelper.Store(this.RootNodeBlockNumber, header, index);
index += StoredConstants.LongLength;
// 空闲块头序号 8 Bytes
StoredHelper.Store(this.FreeBlockHeadNumber, header, index);
index += StoredConstants.LongLength;
return(header);
}
/// <summary>
/// 读取块存储头部
/// </summary>
private void ReadFileHeader()
{
byte[] header = new byte[this.FileHeaderSize];
this.Stream.Seek(this.SeekStart, SeekOrigin.Begin);
this.Stream.Read(header, 0, this.FileHeaderSize);
int index = 0;
// 魔数前缀
foreach (byte b in FileHeaderPrefix)
{
if (header[index] != b)
{
throw new LinkedFileException("invalid header prefix");
}
index++;
}
// 块的大小
this.BlockSize = StoredHelper.RetrieveInt(header, index);
index += StoredConstants.IntegerLength;
// 空闲列表头序号
this.FreeBlockHead = StoredHelper.RetrieveLong(header, index);
index += StoredConstants.LongLength;
this.IsHeaderDirty = false;
if (this.BlockSize < StoredConstants.MinBlockSize)
{
throw new LinkedFileException("linked file block size too small " + this.BlockSize);
}
}
/// <summary>
/// 读取块存储头部
/// </summary>
private void ReadFileHeader()
{
// 魔数前缀长度 | 块的大小
byte[] header = new byte[FileHeaderSize];
this.Stream.Seek(this.SeekStart, SeekOrigin.Begin);
this.Stream.Read(header, 0, FileHeaderSize);
int index = 0;
// 魔数前缀
foreach (byte b in FileHeaderPrefix)
{
if (header[index] != b)
{
throw new BlockFileException("Invalid block file header prefix.");
}
index++;
}
// 块的大小 4 Bytes
this.BlockSize = StoredHelper.RetrieveInt(header, index);
index += StoredConstants.IntegerLength;
if (this.BlockSize < StoredConstants.MinBlockSize)
{
throw new BlockFileException("Block size is too small " + this.BlockSize + ".");
}
}
/// <summary>
/// 获取指定头序号的大块数据
/// </summary>
/// <param name="headBlockNumber">指定头序号</param>
/// <returns>大块数据</returns>
public byte[] GetChunk(long headBlockNumber)
{
// get the head, interpret the length
LinkedFileBlockFlag blockFlag;
long nextBlockNumber;
byte[] block = this.ReadBlock(headBlockNumber, out blockFlag, out nextBlockNumber);
// 读取块长度
int length = StoredHelper.RetrieveInt(block, 0);
if (length < 0)
{
throw new LinkedFileException("negative length block? must be garbage: " + length);
}
if (blockFlag != LinkedFileBlockFlag.Head)
{
throw new LinkedFileException("first block not marked HEAD");
}
byte[] buffer = new byte[length];
// 在第一个块中读取数据
int firstLength = this.BlockSize - StoredConstants.IntegerLength;
if (firstLength > length)
{
firstLength = length;
}
Array.Copy(block, StoredConstants.IntegerLength, buffer, 0, firstLength);
// 在链接的其他块中读取数据
int stored = firstLength;
while (stored < length)
{
// get the next buffer
long currentBlockNumber = nextBlockNumber;
block = this.ReadBlock(currentBlockNumber, out blockFlag, out nextBlockNumber);
int nextLength = this.BlockSize;
if (length - stored < nextLength)
{
nextLength = length - stored;
}
Array.Copy(block, 0, buffer, stored, nextLength);
stored += nextLength;
}
return(buffer);
}
/// <summary>
/// 构造存储头
/// </summary>
/// <returns></returns>
public byte[] MakeFileHeader()
{
// 魔数前缀长度 | 块的大小
byte[] header = new byte[FileHeaderSize];
// 魔数前缀
FileHeaderPrefix.CopyTo(header, 0);
// 块的大小 4 Bytes
StoredHelper.Store(this.BlockSize, header, FileHeaderPrefix.Length);
return(header);
}
/// <summary>
/// 读取B+树存储头
/// </summary>
private void ReadHeader()
{
// 魔数前缀 | 版本 | 节点容量 | 键大小 | 根节点块序号 | 空闲块头序号
// prefix | version | node size | key size | block number of root | block number of free list head
byte[] header = new byte[HeaderSize];
this.Stream.Seek(this.SeekStart, SeekOrigin.Begin);
this.Stream.Read(header, 0, HeaderSize);
// 验证头前缀魔数
int index = 0;
foreach (byte b in StoredConstants.TreeFileHeaderPrefix)
{
if (header[index] != b)
{
throw new BlockFileException("invalid header prefix");
}
index++;
}
// 版本
this.Version = header[index];
index += 1;
// 节点容量
this.NodeCapacity = StoredHelper.RetrieveInt(header, index);
index += StoredConstants.IntegerLength;
// 键大小
this.KeyLength = StoredHelper.RetrieveInt(header, index);
index += StoredConstants.IntegerLength;
// 根节点块序号
this.RootNodeBlockNumber = StoredHelper.RetrieveLong(header, index);
index += StoredConstants.LongLength;
// 空闲块头序号
this.FreeBlockHeadNumber = StoredHelper.RetrieveLong(header, index);
index += StoredConstants.LongLength;
if (this.NodeCapacity < 2)
{
throw new BPlusTreeException("node size must be larger than 2");
}
if (this.KeyLength < 5)
{
throw new BPlusTreeException("Key length must be larger than 5");
}
}
/// <summary>
/// 在指定的块序号之后，查找新的空闲块头序号
/// </summary>
/// <param name="blockNumber">指定的块序号</param>
/// <returns>新的空闲块头序号</returns>
private long ParseFreeBlock(long blockNumber)
{
int freeSize = 1 + StoredConstants.LongLength;
byte[] block = new byte[freeSize];
this.BlockFile.ReadBlock(blockNumber, block, 0, freeSize);
if (block[0] != (byte)BPlusTreeNodeIndicator.Free)
{
throw new BPlusTreeException("free block not marked free");
}
long newHead = StoredHelper.RetrieveLong(block, 1);
return(newHead);
}
/// <summary>
/// 读取块
/// </summary>
/// <param name="blockNumber">块序号</param>
/// <param name="blockFlag">块标记</param>
/// <param name="nextBlockNumber">链接的下一个块</param>
/// <returns>块数据</returns>
private byte[] ReadBlock(long blockNumber, out LinkedFileBlockFlag blockFlag, out long nextBlockNumber)
{
byte[] fullBuffer = new byte[LinkedBlockOverhead + this.BlockSize];
this.BlockFile.ReadBlock(blockNumber, fullBuffer, 0, fullBuffer.Length);
// 读取块标记
blockFlag = (LinkedFileBlockFlag)fullBuffer[0];
// 读取链接的下一个块的序号
nextBlockNumber = StoredHelper.RetrieveLong(fullBuffer, 1);
// 读取数据
byte[] buffer = new byte[this.BlockSize];
Array.Copy(fullBuffer, LinkedBlockOverhead, buffer, 0, this.BlockSize);
return(buffer);
}
/// <summary>
/// 构造存储头
/// </summary>
/// <returns></returns>
public byte[] MakeFileHeader()
{
// 魔数前缀长度 | 块的大小 | 空闲列表头序号
byte[] header = new byte[this.FileHeaderSize];
// 魔数前缀
FileHeaderPrefix.CopyTo(header, 0);
int index = FileHeaderPrefix.Length;
// 块的大小
StoredHelper.Store(this.BlockSize, header, index);
index += StoredConstants.IntegerLength;
// 空闲列表头序号
StoredHelper.Store(this.FreeBlockHead, header, index);
index += StoredConstants.LongLength;
return(header);
}
/// <summary>
/// 回收再利用指定序号的块
/// </summary>
/// <param name="blockNumber">指定序号</param>
public void ReclaimBlock(long blockNumber)
{
int freeSize = 1 + StoredConstants.LongLength;
byte[] block = new byte[freeSize];
// it better not already be marked free
this.BlockFile.ReadBlock(blockNumber, block, 0, 1);
if (block[0] == (byte)BPlusTreeNodeIndicator.Free)
{
throw new BPlusTreeException("attempt to re-free free block not allowed");
}
block[0] = (byte)BPlusTreeNodeIndicator.Free;
// 将指定序号的块置为空闲
StoredHelper.Store(this.FreeBlockHeadNumber, block, 1);
this.BlockFile.WriteBlock(blockNumber, block, 0, freeSize);
this.FreeBlockHeadNumber = blockNumber;
}
/// <summary>
/// 写入块
/// </summary>
/// <param name="blockNumber">块序号</param>
/// <param name="blockFlag">块标记</param>
/// <param name="fromArray">读取至此数组</param>
/// <param name="startAt">读取起始点</param>
/// <param name="length">读取长度</param>
/// <param name="nextBlockNumber">链接的下一个块</param>
private void WriteBlock(long blockNumber, LinkedFileBlockFlag blockFlag, byte[] fromArray, int startAt, int length, long nextBlockNumber)
{
if (this.BlockSize < length)
{
throw new LinkedFileException("block size too small " + this.BlockSize + "<" + length);
}
byte[] buffer = new byte[LinkedBlockOverhead + length];
// 写入块标记
buffer[0] = (byte)blockFlag; // 1 Byte
// 写入链接的下一个块的序号
StoredHelper.Store(nextBlockNumber, buffer, 1); // 8 Bytes
// 写入数据
if (fromArray != null)
{
Array.Copy(fromArray, startAt, buffer, LinkedBlockOverhead, length);
}
this.BlockFile.WriteBlock(blockNumber, buffer, 0, buffer.Length);
}
/// <summary>
/// 存储新的大块数据，返回头序号。
/// </summary>
/// <param name="chunk">读取至此数组</param>
/// <param name="startAt">读取起始点</param>
/// <param name="length">读取长度</param>
/// <returns>存储数据的头序号</returns>
public long StoreChunk(byte[] chunk, int startAt, int length)
{
if (length < 0 || startAt < 0)
{
throw new LinkedFileException("cannot store negative length chunk (" + startAt + "," + length + ")");
}
// 分配用于存储的块 并标记为头块
long currentBlockNumber = this.AllocateBlock();
LinkedFileBlockFlag currentBlockFlag = LinkedFileBlockFlag.Head;
// 存储数据的头序号
long headBlockNumber = currentBlockNumber;
int endAt = startAt + length;
// special case: zero length chunk
if (endAt > chunk.Length)
{
throw new LinkedFileException("array doesn't have this much data: " + endAt);
}
// store header with length information
byte[] block = new byte[this.BlockSize];
// 存储块长度
StoredHelper.Store(length, block, 0);
int fromIndex = startAt;
int firstBlockLength = this.BlockSize - StoredConstants.IntegerLength;
int storedLength = 0;
if (firstBlockLength > length)
{
firstBlockLength = length;
}
// 存储数据
Array.Copy(chunk, fromIndex, block, StoredConstants.IntegerLength, firstBlockLength);
storedLength += firstBlockLength;
fromIndex += firstBlockLength;
// 存储剩余数据
while (storedLength < length)
{
// 获取下一个块序号
long nextBlockNumber = this.AllocateBlock();
// 存储当前数据
this.WriteBlock(currentBlockNumber, currentBlockFlag, block, 0, block.Length, nextBlockNumber);
currentBlockNumber = nextBlockNumber;
currentBlockFlag = LinkedFileBlockFlag.Body; // 下一个块则为Body
int nextLength = this.BlockSize;
if (storedLength + nextLength > length)
{
nextLength = length - storedLength;
}
Array.Copy(chunk, fromIndex, block, 0, nextLength);
storedLength += nextLength;
fromIndex += nextLength;
}
// 存储最终块
this.WriteBlock(currentBlockNumber, currentBlockFlag, block, 0, block.Length, StoredConstants.NullBlockNumber);
return(headBlockNumber);
}