Method Prefetch

table/block_based_table_reader.cc:2557–2613

}

Status BlockBasedTable::Prefetch(const Slice* const begin,
                                 const Slice* const end) {
  auto& comparator = rep_->internal_comparator;
  auto user_comparator = comparator.user_comparator();
  // pre-condition
  if (begin && end && comparator.Compare(*begin, *end) > 0) {
    return Status::InvalidArgument(*begin, *end);
  }

  IndexBlockIter iiter_on_stack;
  auto iiter = NewIndexIterator(ReadOptions(), false, &iiter_on_stack);
  std::unique_ptr<InternalIteratorBase<BlockHandle>> iiter_unique_ptr;
  if (iiter != &iiter_on_stack) {
    iiter_unique_ptr =
        std::unique_ptr<InternalIteratorBase<BlockHandle>>(iiter);
  }

  if (!iiter->status().ok()) {
    // error opening index iterator
    return iiter->status();
  }

  // indicates if we are on the last page that need to be pre-fetched
  bool prefetching_boundary_page = false;

  for (begin ? iiter->Seek(*begin) : iiter->SeekToFirst(); iiter->Valid();
       iiter->Next()) {
    BlockHandle block_handle = iiter->value();
    const bool is_user_key =
        rep_->found_table_properties &&
        rep_->table_properties_base.index_key_is_user_key > 0;
    if (end &&
        ((!is_user_key && comparator.Compare(iiter->key(), *end) >= 0) ||
         (is_user_key &&
          user_comparator->Compare(iiter->key(), ExtractUserKey(*end)) >= 0))) {
      if (prefetching_boundary_page) {
        break;
      }

      // The index entry represents the last key in the data block.
      // We should load this page into memory as well, but no more
      prefetching_boundary_page = true;
    }

    // Load the block specified by the block_handle into the block cache
    DataBlockIter biter;
    NewDataBlockIterator<DataBlockIter>(rep_, ReadOptions(), block_handle,
                                        &biter);

    if (!biter.status().ok()) {
      // there was an unexpected error while pre-fetching
      return biter.status();
    }
  }

  return Status::OK();
}