def METHOD_NAME(self):
    dbs = self.fetch_dbs()
    mapper = self.get_mapper()
    db_ids = [str(db.id) for db in dbs]
    db_ids_to_add = list(set(db_ids) - set(mapper.values()))
    mapper = self.bulk_add(db_ids_to_add, mapper)
    db_ids_to_pop = set(mapper.values()) - set(db_ids)
    mapper = self.bulk_pop(db_ids_to_pop, mapper)
    self.set_mapper(mapper)
    if settings.DEBUG:
        logger.debug("Oracle listen ports: {}".format(len(mapper.keys())))