mysql中的直方图采样逻辑

int handler::sample_next(uchar *buf) {
  // Temporary set inited to RND, since we are calling rnd_next().
  int res = rnd_next(buf);

  std::uniform_real_distribution<double> rnd(0.0, 1.0);
  while (!res && rnd(m_random_number_engine) > (m_sampling_percentage / 100.0))
    res = rnd_next(buf);

  return res;
}