code: public function gc($force = false)
      {
          if ($force || mt_rand(0, 1000000) < $this->gcProbability) {
              $this->db->createCommand()
                  ->delete($this->cacheTable, '[[expire]] > 0 AND [[expire]] < ' . time())
                  ->execute();
          }
      }
docs: Removes the expired data values.
  @param bool $force whether to enforce the garbage collection regardless of [[gcProbability]].
  Defaults to false, meaning the actual deletion happens with the probability as specified by [[gcProbability]].