code: func (s *Server) newTikvHandlerTool() *tikvHandlerTool {
  	var tikvStore tikv.Storage
  	store, ok := s.driver.(*TiDBDriver)
  	if !ok {
  		panic("Invalid KvStore with illegal driver")
  	}
  
  	if tikvStore, ok = store.store.(tikv.Storage); !ok {
  		panic("Invalid KvStore with illegal store")
  	}
  
  	regionCache := tikvStore.GetRegionCache()
  
  	return &tikvHandlerTool{
  		helper.Helper{
  			RegionCache: regionCache,
  			Store:       tikvStore,
  		},
  	}
  }
docs: // newTikvHandlerTool checks and prepares for tikv handler.
  // It would panic when any error happens.