Method tryFlatten

source/core/StarBTreeDatabase.cpp:1138–1193

}

bool BTreeDatabase::tryFlatten() {
  if (m_headFreeIndexBlock == InvalidBlockIndex || m_rootIsLeaf || !m_device->isWritable())
    return false;
  
  BlockIndex freeBlockCount = 0;
  BlockIndex indexBlockIndex = m_headFreeIndexBlock;
  while (indexBlockIndex != InvalidBlockIndex) {
    FreeIndexBlock indexBlock = readFreeIndexBlock(indexBlockIndex);
    freeBlockCount += 1 + indexBlock.freeBlocks.size();
    indexBlockIndex = indexBlock.nextFreeBlock;
  }

  BlockIndex expectedBlockCount = (m_deviceSize - HeaderSize) / m_blockSize;
  float free = float(freeBlockCount) / float(expectedBlockCount);
  if (free < 0.05f)
    return false;

  Logger::info("[BTreeDatabase] File '{}' is {:.2f}% free space, flattening", m_device->deviceName(), free * 100.f);

  indexBlockIndex = m_headFreeIndexBlock;
  {
    List<BlockIndex> availableBlocksList;
    do {
      FreeIndexBlock indexBlock = readFreeIndexBlock(indexBlockIndex);
      availableBlocksList.appendAll(indexBlock.freeBlocks);
      availableBlocksList.append(indexBlockIndex);
      indexBlockIndex = indexBlock.nextFreeBlock;
    } while (indexBlockIndex != InvalidBlockIndex);
    m_headFreeIndexBlock = InvalidBlockIndex;

    sort(availableBlocksList);
    for (auto& availableBlock : availableBlocksList)
      m_availableBlocks.insert(m_availableBlocks.end(), availableBlock);
  }

  BlockIndex count = 1; // 1 to include root index

  double start = Time::monotonicTime();
  auto index = m_impl.loadIndex(m_impl.rootPointer());
  if (flattenVisitor(index, count)) {
    m_impl.deleteIndex(index);
    index->self = InvalidBlockIndex;
    m_root = m_impl.storeIndex(index);
  }

  m_availableBlocks.clear();
  m_device->resize(m_deviceSize = HeaderSize + (StreamOffset)m_blockSize * count);

  m_indexCache.clear();
  commitWrites();
  writeRoot();
  m_uncommitted.clear();

  Logger::info("[BTreeDatabase] Finished flattening '{}' in {:.2f} milliseconds", m_device->deviceName(), (Time::monotonicTime() - start) * 1000.f);
  return true;
}

bool BTreeDatabase::flattenVisitor(BTreeImpl::Index& index, BlockIndex& count) {