message: Don't acquire buffer manager lock for block reads
diff: @@ -45,10 +45,6 @@ unique_ptr<BufferHandle> BlockHandle::Load(shared_ptr<BlockHandle> &handle) {
  auto &buffer_manager = BufferManager::GetBufferManager(handle->db);
  auto &block_manager = BlockManager::GetBlockManager(handle->db);
  if (handle->block_id < MAXIMUM_BLOCK) {
  - // FIXME: currently we still require a lock for reading blocks from disk
  - // this is mainly down to the block manager only having a single pointer into the file
  - // this is relatively easy to fix later on
  - lock_guard<mutex> buffer_lock(buffer_manager.manager_lock);
  auto block = make_unique<Block>(Allocator::Get(handle->db), handle->block_id);
  block_manager.Read(*block);
  handle->buffer = move(block);
  