leveldb源码分析--SSTable之TableBuilder

Status TableBuilder::Finish() {

  //先将data_block内容写到文件
  Flush();

  // 写filterblock也即为Metablock记录的filter信息，具体分析稍后再filterblock中专门分析
  if (ok() && r->filter_block != NULL) {
    WriteRawBlock(r->filter_block->Finish(), kNoCompression,
                  &filter_block_handle);
  }

  // 写入metablock的index，包含一个key=filter.filter名，value=开始的filter_block的handle
  if (ok()) {
    BlockBuilder meta_index_block(&r->options);
    if (r->filter_block != NULL) {
      std::string key = "filter.";
      key.append(r->options.filter_policy->Name());
      std::string handle_encoding;
      filter_block_handle.EncodeTo(&handle_encoding);
     meta_index_block.Add(key, handle_encoding);
    }
    // 写入文件中
    WriteBlock(&meta_index_block, &metaindex_block_handle);
  }

  // 写data_block的索引块，之前每个data_block会取一个FindShortestSeparator作为key，
  // value为该block的block_handle，最后一块的key为FindShortSuccessor
  if (ok()) {
    if (r->pending_index_entry) {
      r->options.comparator->FindShortSuccessor(&r->last_key);
      std::string handle_encoding;
      r->pending_handle.EncodeTo(&handle_encoding);
      r->index_block.Add(r->last_key, Slice(handle_encoding));
      r->pending_index_entry = false;
    }
    WriteBlock(&r->index_block, &index_block_handle);
  }

  // 写footer块，包括了MetaIndex block和Indexblock 的BlockHandle，以及填充区和一个magic数字
  if (ok()) {
    Footer footer;
    footer.set_metaindex_handle(metaindex_block_handle);
    footer.set_index_handle(index_block_handle);
    footer.EncodeTo(&footer_encoding);
    r->status = r->file->Append(footer_encoding);
    if (r->status.ok()) {
      r->offset += footer_encoding.size();
    }
  }
  return r->status;
}