code: func (gvc *GlobalVariableCache) Get() (succ bool, rows []chunk.Row, fields []*ast.ResultField) {
  	gvc.RLock()
  	defer gvc.RUnlock()
  	if time.Since(gvc.lastModify) < globalVariableCacheExpiry {
  		succ, rows, fields = !gvc.disable, gvc.rows, gvc.fields
  		return
  	}
  	succ = false
  	return
  }
docs: // Get gets the global variables from cache.