code: public NutTxDao rollback(String id) {
          if (debug)
              log.debugf("rollback id=%s", id);
          try {
              Savepoint sp = sps.getAs(id, Savepoint.class);
              if (sp != null)
                  conn.rollback(sp);
              else
                  log.debug("Null Savepoint found, skip, id=" + id);
          }
          catch (Throwable e) {
          }
          return this;
      }
docs: 回滚事务
  
  @param id
  回滚点
  @return 原对象