code: def _check_rename_constraints(self, old_key, new_key):
          
          if new_key in self.relations:
              dbt.exceptions.raise_cache_inconsistent(
                  'in rename, new key {} already in cache: {}'
                  .format(new_key, list(self.relations.keys()))
              )
  
          if old_key not in self.relations:
              logger.debug(
                  'old key {} not found in self.relations, assuming temporary'
                  .format(old_key)
              )
              return False
          return True
docs: Check the rename constraints, and return whether or not the rename
          can proceed.
  
          If the new key is already present, that is an error.
          If the old key is absent, we debug log and return False, assuming it's
          a temp table being renamed.
  
          :param _ReferenceKey old_key: The existing key, to rename from.
          :param _ReferenceKey new_key: The new key, to rename to.
          :return bool: If the old relation exists for renaming.
          :raises InternalError: If the new key is already present.