code: func (n *Node) OpenDatabase(name string, cache, handles int, namespace string) (ethdb.Database, error) {
  	if n.config.DataDir == "" {
  		return rawdb.NewMemoryDatabase(), nil
  	}
  	return rawdb.NewLevelDBDatabase(n.config.ResolvePath(name), cache, handles, namespace)
  }
docs: // OpenDatabase opens an existing database with the given name (or creates one if no
  // previous can be found) from within the node's instance directory. If the node is
  // ephemeral, a memory database is returned.