活动开场一秒上千次提交，后台多出一倍重复记录：轻应用的幂等键、请求令牌与重试防重实践

let submitting = false;
let idemToken = null;

// 进入页面时先向后端申请本次提交的幂等令牌
async function fetchToken(activityId) {
  const res = await fetch(`/api/idem-token?activityId=${activityId}`);
  const data = await res.json();
  idemToken = data.token;
  return idemToken;
}

async function submit(form) {
  if (submitting) return;          // 挡住同页面的连点
  if (!idemToken) await fetchToken(form.activityId);
  submitting = true;
  try {
    const res = await fetch('/api/signup', {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ ...form, idemToken }),
    });
    const data = await res.json();
    if (data.ok) { location.href = '/success'; }
    else { submitting = false; idemToken = null; alert(data.msg); }
  } catch (e) {
    // 关键：超时重试必须复用同一个 idemToken，不能在这里重新申请
    submitting = false;
  }
}

import redis, json, uuid

r = redis.Redis(host='localhost', port=6379, db=0)

def signup(user_id, activity_id, idem_token, payload):
    # 令牌键：拦截同一次提交的连点/重试
    token_key = f'idem:signup:{idem_token}'
    # 业务键：拦截跨设备、跨页面的真实重复
    biz_key = f'biz:signup:{user_id}:{activity_id}'

    # SET NX：只有第一个请求能占位成功，EX 兜底过期
    got = r.set(token_key, 'PROCESSING', nx=True, ex=300)
    if not got:
        state = r.get(token_key)
        if state == b'PROCESSING':
            return {'ok': False, 'msg': '正在处理，请勿重复提交'}
        return json.loads(r.get(token_key + ':resp') or b'{}')  # 返回首次结果

    if r.exists(biz_key):
        r.set(token_key, 'DUP', ex=300)
        return {'ok': False, 'msg': '您已经报过名了'}

    try:
        order_id = do_insert(user_id, activity_id, payload)   # 内部走唯一索引
        r.set(biz_key, order_id, nx=True, ex=86400)
        resp = {'ok': True, 'orderId': order_id}
        r.set(token_key + ':resp', json.dumps(resp), ex=86400)
        r.set(token_key, 'DONE', ex=86400)
        return resp
    except Exception:
        r.delete(token_key)          # 失败释放，允许用户重试
        raise

CREATE UNIQUE INDEX uk_user_activity
ON signup_record(user_id, activity_id, biz_dimension);

CREATE TABLE mq_consume_log (
  msg_id      VARCHAR(64) PRIMARY KEY,
  consumed_at DATETIME NOT NULL
);
-- 消费前先 INSERT IGNORE：插入成功才处理，已存在说明是重复投递直接 ACK