message: Only add handle to eviction queue when there are no more readers left
diff: @@ -192,10 +192,12 @@ void BufferManager::Unpin(shared_ptr<BlockHandle> &handle) {
  lock_guard<mutex> lock(handle->lock);
  D_ASSERT(handle->readers > 0);
  handle->readers--;
  + if (handle->readers == 0) {
  handle->eviction_timestamp++;
  queue->q.enqueue(make_unique<BufferEvictionNode>(weak_ptr<BlockHandle>(handle), handle->eviction_timestamp));
  // FIXME: do some house-keeping to prevent the queue from being flooded with many old blocks
  }
  +}
  void BufferManager::EvictBlocks(idx_t extra_memory, idx_t memory_limit) {
  unique_ptr<BufferEvictionNode> node;
  