hbase源码系列（九）StoreFile存储格式

private void append(final long memstoreTS, final byte[] key, final int koffset, final int klength,
      final byte[] value, final int voffset, final int vlength)
      throws IOException {
    boolean dupKey = checkKey(key, koffset, klength);
    checkValue(value, voffset, vlength);
    if (!dupKey) {
      //在写每一个新的KeyValue之间，都要检查，到了BlockSize就重新写一个HFileBlock
      checkBlockBoundary();
    }
    //如果当前的fsBlockWriter的状态不对，就重新写一个新块
    if (!fsBlockWriter.isWriting())
      newBlock();

    // 把值写入到ouputStream当中，怎么写入的自己看啊
    {
      DataOutputStream out = fsBlockWriter.getUserDataStream();
      out.writeInt(klength);
      totalKeyLength += klength;
      out.writeInt(vlength);
      totalValueLength += vlength;
      out.write(key, koffset, klength);
      out.write(value, voffset, vlength);
      if (this.includeMemstoreTS) {
        WritableUtils.writeVLong(out, memstoreTS);
      }
    }

    // 记录每个块的第一个key 和 上次写的key
    if (firstKeyInBlock == null) {
      firstKeyInBlock = new byte[klength];
      System.arraycopy(key, koffset, firstKeyInBlock, 0, klength);
    }

    lastKeyBuffer = key;
    lastKeyOffset = koffset;
    lastKeyLength = klength;
    entryCount++;
  }

public void close() throws IOException {
    if (outputStream == null) {
      return;
    }
    // 经过编码压缩的，把编码压缩方式写进FileInfo里面
    blockEncoder.saveMetadata(this);
    //结束块
    finishBlock();
    //输出DataBlockIndex索引的非root层信息
    writeInlineBlocks(true);

    FixedFileTrailer trailer = new FixedFileTrailer(2,HFileReaderV2.MAX_MINOR_VERSION);

    // 如果有meta块的存在的话
    if (!metaNames.isEmpty()) {
      for (int i = 0; i < metaNames.size(); ++i) {
        long offset = outputStream.getPos();
        // 输出meta的内容，它是meta的名字的集合，按照名字排序
        DataOutputStream dos = fsBlockWriter.startWriting(BlockType.META);
        metaData.get(i).write(dos);

        fsBlockWriter.writeHeaderAndData(outputStream);
        totalUncompressedBytes += fsBlockWriter.getUncompressedSizeWithHeader();

        // 把meta块的信息加到meta块的索引里
        metaBlockIndexWriter.addEntry(metaNames.get(i), offset,
            fsBlockWriter.getOnDiskSizeWithHeader());
      }
    }

    //下面这部分是打开文件的时候就加载的部分，是前面部分的索引
    //HFileBlockIndex的根层次的索引
    long rootIndexOffset = dataBlockIndexWriter.writeIndexBlocks(outputStream);
    trailer.setLoadOnOpenOffset(rootIndexOffset);

    //Meta块的索引
    metaBlockIndexWriter.writeSingleLevelIndex(fsBlockWriter.startWriting(
        BlockType.ROOT_INDEX), "meta");
    fsBlockWriter.writeHeaderAndData(outputStream);
    totalUncompressedBytes += fsBlockWriter.getUncompressedSizeWithHeader();

    //如果需要写入Memstore的最大时间戳到FileInfo里面
    if (this.includeMemstoreTS) {
      appendFileInfo(MAX_MEMSTORE_TS_KEY, Bytes.toBytes(maxMemstoreTS));
      appendFileInfo(KEY_VALUE_VERSION, Bytes.toBytes(KEY_VALUE_VER_WITH_MEMSTORE));
    }

    //把FileInfo的起始位置写入trailer，然后输出
    writeFileInfo(trailer, fsBlockWriter.startWriting(BlockType.FILE_INFO));
    fsBlockWriter.writeHeaderAndData(outputStream);
    totalUncompressedBytes += fsBlockWriter.getUncompressedSizeWithHeader();

    // 输出GENERAL_BLOOM_META、DELETE_FAMILY_BLOOM_META类型的BloomFilter的信息
    for (BlockWritable w : additionalLoadOnOpenData){
      fsBlockWriter.writeBlock(w, outputStream);
      totalUncompressedBytes += fsBlockWriter.getUncompressedSizeWithHeader();
    }

    //HFileBlockIndex的二级实体的层次
    trailer.setNumDataIndexLevels(dataBlockIndexWriter.getNumLevels());
    //压缩前的HFileBlockIndex的大小
    trailer.setUncompressedDataIndexSize(
        dataBlockIndexWriter.getTotalUncompressedSize());
    //第一个HFileBlock的起始位置
    trailer.setFirstDataBlockOffset(firstDataBlockOffset);
    //最后一个HFileBlock的起始位置
    trailer.setLastDataBlockOffset(lastDataBlockOffset);
    //比较器的类型
    trailer.setComparatorClass(comparator.getClass());
    //HFileBlockIndex的根实体的数量，应该是和HFileBlock的数量是一样的
    //它每次都把HFileBlock的第一个key加进去
    trailer.setDataIndexCount(dataBlockIndexWriter.getNumRootEntries());

    //把Trailer的信息写入硬盘，关闭输出流
    finishClose(trailer);

    fsBlockWriter.release();
  }

this.fileStatus = fileStatus;
    Path p = fileStatus.getPath();
    if (HFileLink.isHFileLink(p)) {
      // HFileLink 被判断出来它是HFile
      this.reference = null;
      this.link = new HFileLink(conf, p);
    } else if (isReference(p)) {
      this.reference = Reference.read(fs, p);
      //关联的地址也可能是一个HFileLink，snapshot的时候介绍了
      Path referencePath = getReferredToFile(p);
      if (HFileLink.isHFileLink(referencePath)) {
        // HFileLink Reference 如果它是一个HFileLink型的
        this.link = new HFileLink(conf, referencePath);
      } else {
        // 只是引用
        this.link = null;
      }
    } else if (isHFile(p)) {
      // HFile
      this.reference = null;
      this.link = null;
    } else {
      throw new IOException("path=" + p + " doesn‘t look like a valid StoreFile");
    }

for (Path path: fileLink.getLocations()) {
        if (path.equals(currentPath)) continue;
        try {
          in = fs.open(path, bufferSize);
          in.seek(pos);
          assert(in.getPos() == pos) : "Link unable to seek to the right position=" + pos;
          if (LOG.isTraceEnabled()) {
            if (currentPath != null) {
              LOG.debug("link open path=" + path);
            } else {
              LOG.trace("link switch from path=" + currentPath + " to path=" + path);
            }
          }
          currentPath = path;
          return(in);
        } catch (FileNotFoundException e) {
          // Try another file location
        }
}