秒杀高并发解决方案

1.秒杀/高并发方案-介绍

秒杀/高并发其实主要解决两个问题，一个是并发读，一个是并发写
并发读的核心优化理念是尽量减少用户到 DB 来"读"数据，或者让他们读更少的数据, 并发写的处理原则也一样
针对秒杀系统需要做一些保护，针对意料之外的情况设计兜底方案，以防止最坏的情况发生。
系统架构要满足高可用: 流量符合预期时要稳定，要保证秒杀活动顺利完成，即秒杀商品顺利地卖出去，这个是最基本的前提
系统保证数据的一致性: 就是秒杀 10 个商品，那就只能成交 10 个商品，多一个少一个都不行。一旦库存不对，就要承担损失
系统要满足高性能: 也就是系统的性能要足够高，需要支撑大流量, 不光是服务端要做极致的性能优化，而且在整个请求链路上都要做协同的优化，每个地方快一点, 整个系统就"快 "了
秒杀涉及大量的并发读和并发写，因此支持高并发访问这点非常关键, 对应的方案比如页面缓存方案、Redis 预减库存/内存标记与隔离、请求的削峰(RabbitMQ/异步请求)、分布式 Session 共享等

2.秒杀场景模拟

这里模拟每秒1000个请求，循环10次即总共发起10000次请求，请求/seckill/doSeckill接口

3.秒杀解决方案

3.1 v1.0-原始版本

SeckillController

java

@Controller
@RequestMapping(value = "/seckill")
public class SeckillController {

    @Resource
    private GoodsService goodsService;

    @Resource
    private SeckillOrderService seckillOrderService;

    @Resource
    private OrderService orderService;

    @RequestMapping(value = "/doSeckill")
    public String doSeckill(Model model, User user, Long goodsId) {
        System.out.println("-----秒杀 V1.0--------");
        //===================秒杀 v1.0 start =========================
        if (user == null) {
            return "login";
        }
        model.addAttribute("user", user);
        GoodsVo goodsVo = goodsService.findGoodsVoByGoodsId(goodsId);
        //判断库存
        if (goodsVo.getStockCount() < 1) {
            model.addAttribute("errmsg", RespBeanEnum.ENTRY_STOCK.getMessage());
            return "secKillFail";
        }
        //解决重复抢购
        LambdaQueryWrapper<SeckillOrder> seckillOrderLambdaQueryWrapper = new QueryWrapper<SeckillOrder>().lambda()
                .eq(SeckillOrder::getGoodsId, goodsId).eq(SeckillOrder::getUserId, user.getId());
        SeckillOrder seckillOrder = seckillOrderService.getOne(seckillOrderLambdaQueryWrapper);
        if (seckillOrder != null) {
            model.addAttribute("errmsg", RespBeanEnum.REPEATE_ERROR.getMessage());
            return "secKillFail";
        }
        //抢购
        Order order = orderService.seckill(user, goodsVo);
        if (order == null) {
            model.addAttribute("errmsg", RespBeanEnum.ENTRY_STOCK.getMessage());
            return "secKillFail";
        }
        model.addAttribute("order", order);
        model.addAttribute("goods", goodsVo);
        return "orderDetail";
        //===================秒杀 v1.0 end... =========================
    }

}

@Controller
@RequestMapping(value = "/seckill")
public class SeckillController {

    @Resource
    private GoodsService goodsService;

    @Resource
    private SeckillOrderService seckillOrderService;

    @Resource
    private OrderService orderService;

    @RequestMapping(value = "/doSeckill")
    public String doSeckill(Model model, User user, Long goodsId) {
        System.out.println("-----秒杀 V1.0--------");
        //===================秒杀 v1.0 start =========================
        if (user == null) {
            return "login";
        }
        model.addAttribute("user", user);
        GoodsVo goodsVo = goodsService.findGoodsVoByGoodsId(goodsId);
        //判断库存
        if (goodsVo.getStockCount() < 1) {
            model.addAttribute("errmsg", RespBeanEnum.ENTRY_STOCK.getMessage());
            return "secKillFail";
        }
        //解决重复抢购
        LambdaQueryWrapper<SeckillOrder> seckillOrderLambdaQueryWrapper = new QueryWrapper<SeckillOrder>().lambda()
                .eq(SeckillOrder::getGoodsId, goodsId).eq(SeckillOrder::getUserId, user.getId());
        SeckillOrder seckillOrder = seckillOrderService.getOne(seckillOrderLambdaQueryWrapper);
        if (seckillOrder != null) {
            model.addAttribute("errmsg", RespBeanEnum.REPEATE_ERROR.getMessage());
            return "secKillFail";
        }
        //抢购
        Order order = orderService.seckill(user, goodsVo);
        if (order == null) {
            model.addAttribute("errmsg", RespBeanEnum.ENTRY_STOCK.getMessage());
            return "secKillFail";
        }
        model.addAttribute("order", order);
        model.addAttribute("goods", goodsVo);
        return "orderDetail";
        //===================秒杀 v1.0 end... =========================
    }

}

OrderServiceImpl

java

@Service
public class OrderServiceImpl extends ServiceImpl<OrderMapper, Order> implements OrderService {

    @Resource
    private SecKillGoodsService secKillGoodsService;

    @Resource
    private OrderMapper orderMapper;

    @Resource
    private SeckillOrderMapper seckillOrderMapper;

    /**
     * 秒杀商品，减少库存
     * @param user
     * @param goodsVo
     * @return
     */
    @Override
    public Order seckill(User user, GoodsVo goodsVo) {
        //1.根据商品id获取秒杀商品信息
        LambdaQueryWrapper<SecKillGoods> lambdaQueryWrapper = new QueryWrapper<SecKillGoods>().lambda().eq(SecKillGoods::getGoodsId,goodsVo.getId());
        SecKillGoods seckillGoods = secKillGoodsService.getOne(lambdaQueryWrapper);
        //2.秒杀商品库存-1
        seckillGoods.setStockCount(seckillGoods.getStockCount() - 1);
        secKillGoodsService.updateById(seckillGoods);
        //3.生成普通订单
        Order order = new Order();
        order.setUserId(user.getId());
        order.setGoodsId(goodsVo.getId());
        order.setDeliveryAddrId(0L);
        order.setGoodsName(goodsVo.getGoodsName());
        order.setGoodsCount(1);
        order.setGoodsPrice(seckillGoods.getSeckillPrice());
        order.setOrderChannel(1);
        order.setStatus(0);
        order.setCreateDate(new Date());
        orderMapper.insert(order);
        //4.生成秒杀订单
        SeckillOrder seckillOrder = new SeckillOrder();
        seckillOrder.setGoodsId(goodsVo.getId());
        seckillOrder.setUserId(user.getId());
        seckillOrder.setOrderId(order.getId());
        seckillOrderMapper.insert(seckillOrder);
        return order;
    }
}

@Service
public class OrderServiceImpl extends ServiceImpl<OrderMapper, Order> implements OrderService {

    @Resource
    private SecKillGoodsService secKillGoodsService;

    @Resource
    private OrderMapper orderMapper;

    @Resource
    private SeckillOrderMapper seckillOrderMapper;

    /**
     * 秒杀商品，减少库存
     * @param user
     * @param goodsVo
     * @return
     */
    @Override
    public Order seckill(User user, GoodsVo goodsVo) {
        //1.根据商品id获取秒杀商品信息
        LambdaQueryWrapper<SecKillGoods> lambdaQueryWrapper = new QueryWrapper<SecKillGoods>().lambda().eq(SecKillGoods::getGoodsId,goodsVo.getId());
        SecKillGoods seckillGoods = secKillGoodsService.getOne(lambdaQueryWrapper);
        //2.秒杀商品库存-1
        seckillGoods.setStockCount(seckillGoods.getStockCount() - 1);
        secKillGoodsService.updateById(seckillGoods);
        //3.生成普通订单
        Order order = new Order();
        order.setUserId(user.getId());
        order.setGoodsId(goodsVo.getId());
        order.setDeliveryAddrId(0L);
        order.setGoodsName(goodsVo.getGoodsName());
        order.setGoodsCount(1);
        order.setGoodsPrice(seckillGoods.getSeckillPrice());
        order.setOrderChannel(1);
        order.setStatus(0);
        order.setCreateDate(new Date());
        orderMapper.insert(order);
        //4.生成秒杀订单
        SeckillOrder seckillOrder = new SeckillOrder();
        seckillOrder.setGoodsId(goodsVo.getId());
        seckillOrder.setUserId(user.getId());
        seckillOrder.setOrderId(order.getId());
        seckillOrderMapper.insert(seckillOrder);
        return order;
    }
}

说明

非高并发情况下，程序执行流程分析

程序首先校验用户是否登录
然后判断商品库存是充足
在判断是否存在重复抢购
最后执行抢购生成订单及抢购订单数据

高并发情况下,程序执行流程分析

判断商品库存是充足、否存在重复抢购的程序是不具备原子性
秒杀商品的库存为负数，但具体的值无法确定，因为获取秒杀商品库存也不具备原子性
当有多少个请求冲破了前面库存和抢购的过滤，就会去生成多少个订单

3.2 v2.0-秒杀-复购、超卖处理

SeckillController

java

@RequestMapping(value = "/doSeckill")
public String doSeckill(Model model, User user, Long goodsId) {
    System.out.println("-----秒杀 V2.0--------");
    //===================秒杀 v2.0 start =========================
    if (user == null) {
        return "login";
    }
    model.addAttribute("user", user);
    GoodsVo goodsVo = goodsService.findGoodsVoByGoodsId(goodsId);
    //判断库存
    if (goodsVo.getStockCount() < 1) {
        model.addAttribute("errmsg", RespBeanEnum.ENTRY_STOCK.getMessage());
        return "secKillFail";
    }
    //解决重复抢购,直接到redis中获取对应的秒杀订单，如果有则说明已经抢购了，不能继续抢购
    SeckillOrder seckillOrder = (SeckillOrder) redisTemplate.opsForValue().get("order:" + user.getId() + ":" + goodsId);
    if (seckillOrder != null) {
        model.addAttribute("errmsg", RespBeanEnum.REPEATE_ERROR.getMessage());
        return "secKillFail";
    }

    //抢购
    Order order = orderService.seckill(user, goodsVo);
    if (order == null) {
        model.addAttribute("errmsg", RespBeanEnum.ENTRY_STOCK.getMessage());
        return "secKillFail";
    }
    model.addAttribute("order", order);
    model.addAttribute("goods", goodsVo);
    return "orderDetail";
    //===================秒杀 v2.0 end... =========================
}

@RequestMapping(value = "/doSeckill")
public String doSeckill(Model model, User user, Long goodsId) {
    System.out.println("-----秒杀 V2.0--------");
    //===================秒杀 v2.0 start =========================
    if (user == null) {
        return "login";
    }
    model.addAttribute("user", user);
    GoodsVo goodsVo = goodsService.findGoodsVoByGoodsId(goodsId);
    //判断库存
    if (goodsVo.getStockCount() < 1) {
        model.addAttribute("errmsg", RespBeanEnum.ENTRY_STOCK.getMessage());
        return "secKillFail";
    }
    //解决重复抢购,直接到redis中获取对应的秒杀订单，如果有则说明已经抢购了，不能继续抢购
    SeckillOrder seckillOrder = (SeckillOrder) redisTemplate.opsForValue().get("order:" + user.getId() + ":" + goodsId);
    if (seckillOrder != null) {
        model.addAttribute("errmsg", RespBeanEnum.REPEATE_ERROR.getMessage());
        return "secKillFail";
    }

    //抢购
    Order order = orderService.seckill(user, goodsVo);
    if (order == null) {
        model.addAttribute("errmsg", RespBeanEnum.ENTRY_STOCK.getMessage());
        return "secKillFail";
    }
    model.addAttribute("order", order);
    model.addAttribute("goods", goodsVo);
    return "orderDetail";
    //===================秒杀 v2.0 end... =========================
}

OrderServiceImpl

java

/**
 * 秒杀商品，减少库存
 *
 * @param user
 * @param goodsVo
 * @return
 */
@Override
@Transactional(rollbackFor = {Exception.class})
public Order seckill(User user, GoodsVo goodsVo) {
    //1.根据商品id获取秒杀商品信息
    LambdaQueryWrapper<SecKillGoods> lambdaQueryWrapper = new QueryWrapper<SecKillGoods>().lambda().eq(SecKillGoods::getGoodsId, goodsVo.getId());
    SecKillGoods seckillGoods = secKillGoodsService.getOne(lambdaQueryWrapper);
    //2.秒杀商品库存-1
    // seckillGoods.setStockCount(seckillGoods.getStockCount() - 1);
    // secKillGoodsService.updateById(seckillGoods);

    //1. Mysql在默认的事务隔离级别[REPEATABLE-READ]下
    //2. 执行update语句时,会在事务中锁定要更新的行
    //3. 这样可以防止其它会话在同一行执行update,delete
    LambdaUpdateWrapper<SecKillGoods> updateWrapper = new UpdateWrapper<SecKillGoods>().lambda().setSql("stock_count=stock_count-1")
            .eq(SecKillGoods::getGoodsId, goodsVo.getId())
            .gt(SecKillGoods::getStockCount, 0);
    boolean update = secKillGoodsService.update(updateWrapper);
    //如果更新失败说明已经没有库存了
    if (!update) {
        return null;
    }

    //3.生成普通订单
    Order order = new Order();
    order.setUserId(user.getId());
    order.setGoodsId(goodsVo.getId());
    order.setDeliveryAddrId(0L);
    order.setGoodsName(goodsVo.getGoodsName());
    order.setGoodsCount(1);
    order.setGoodsPrice(seckillGoods.getSeckillPrice());
    order.setOrderChannel(1);
    order.setStatus(0);
    order.setCreateDate(new Date());
    orderMapper.insert(order);
    //4.生成秒杀订单
    SeckillOrder seckillOrder = new SeckillOrder();
    seckillOrder.setGoodsId(goodsVo.getId());
    seckillOrder.setUserId(user.getId());
    seckillOrder.setOrderId(order.getId());
    seckillOrderMapper.insert(seckillOrder);

    //设置秒杀订单的key --> order:用户id:商品id
    redisTemplate.opsForValue().set("order:" + user.getId() + ":" + goodsVo.getId(), seckillOrder);
    return order;
}

/**
 * 秒杀商品，减少库存
 *
 * @param user
 * @param goodsVo
 * @return
 */
@Override
@Transactional(rollbackFor = {Exception.class})
public Order seckill(User user, GoodsVo goodsVo) {
    //1.根据商品id获取秒杀商品信息
    LambdaQueryWrapper<SecKillGoods> lambdaQueryWrapper = new QueryWrapper<SecKillGoods>().lambda().eq(SecKillGoods::getGoodsId, goodsVo.getId());
    SecKillGoods seckillGoods = secKillGoodsService.getOne(lambdaQueryWrapper);
    //2.秒杀商品库存-1
    // seckillGoods.setStockCount(seckillGoods.getStockCount() - 1);
    // secKillGoodsService.updateById(seckillGoods);

    //1. Mysql在默认的事务隔离级别[REPEATABLE-READ]下
    //2. 执行update语句时,会在事务中锁定要更新的行
    //3. 这样可以防止其它会话在同一行执行update,delete
    LambdaUpdateWrapper<SecKillGoods> updateWrapper = new UpdateWrapper<SecKillGoods>().lambda().setSql("stock_count=stock_count-1")
            .eq(SecKillGoods::getGoodsId, goodsVo.getId())
            .gt(SecKillGoods::getStockCount, 0);
    boolean update = secKillGoodsService.update(updateWrapper);
    //如果更新失败说明已经没有库存了
    if (!update) {
        return null;
    }

    //3.生成普通订单
    Order order = new Order();
    order.setUserId(user.getId());
    order.setGoodsId(goodsVo.getId());
    order.setDeliveryAddrId(0L);
    order.setGoodsName(goodsVo.getGoodsName());
    order.setGoodsCount(1);
    order.setGoodsPrice(seckillGoods.getSeckillPrice());
    order.setOrderChannel(1);
    order.setStatus(0);
    order.setCreateDate(new Date());
    orderMapper.insert(order);
    //4.生成秒杀订单
    SeckillOrder seckillOrder = new SeckillOrder();
    seckillOrder.setGoodsId(goodsVo.getId());
    seckillOrder.setUserId(user.getId());
    seckillOrder.setOrderId(order.getId());
    seckillOrderMapper.insert(seckillOrder);

    //设置秒杀订单的key --> order:用户id:商品id
    redisTemplate.opsForValue().set("order:" + user.getId() + ":" + goodsVo.getId(), seckillOrder);
    return order;
}

说明

超卖问题处理 前面出现超卖的主要原因在于，更新库存时不具备原子性，这里利用mysql默认的事务隔离级别

[REPEATABLE-READ]在事务中执行update语句获取锁定更新的行，这个机制进行处理

复购（生成了多个订单）问题处理，则在生成订单之前对库存更新进行判断，如果更新失败则不在生成订单

java

//如果更新失败说明已经没有库存了
    if (!update) {
        return null;
    }

//如果更新失败说明已经没有库存了
    if (!update) {
        return null;
    }

优化复购判断 在生成秒杀订单之后将订单存储到redis中，在判断复购时直接从redis中获取，避免频繁查询数据库，提升执行效率

java

//解决重复抢购,直接到redis中获取对应的秒杀订单，如果有则说明已经抢购了，不能继续抢购
    SeckillOrder seckillOrder = (SeckillOrder) redisTemplate.opsForValue().get("order:" + user.getId() + ":" + goodsId);
    if (seckillOrder != null) {
        model.addAttribute("errmsg", RespBeanEnum.REPEATE_ERROR.getMessage());
        return "secKillFail";
    }

//解决重复抢购,直接到redis中获取对应的秒杀订单，如果有则说明已经抢购了，不能继续抢购
    SeckillOrder seckillOrder = (SeckillOrder) redisTemplate.opsForValue().get("order:" + user.getId() + ":" + goodsId);
    if (seckillOrder != null) {
        model.addAttribute("errmsg", RespBeanEnum.REPEATE_ERROR.getMessage());
        return "secKillFail";
    }

测试结果

3.3 v3.0 优化秒杀，Redis 预减库存

前面我们防止超卖是通过到数据库查询和到数据库抢购，来完成的, 代码如下:

如果在短时间内，大量抢购冲击 DB, 造成洪峰, 容易压垮数据库
解决方案: 使用 Redis 完成预减库存，如果没有库存了, 直接返回, 减小对 DB 的压力
示意图：

代码实现

java

@Controller
@RequestMapping(value = "/seckill")
public class SeckillController implements InitializingBean {

    @Resource
    private GoodsService goodsService;

    @Resource
    private SeckillOrderService seckillOrderService;

    @Resource
    private OrderService orderService;

    @Resource
    private RedisTemplate redisTemplate;

    @RequestMapping(value = "/doSeckill")
    public String doSeckill(Model model, User user, Long goodsId) {
        System.out.println("-----秒杀 V3.0--------");
        //===================秒杀 v3.0 start =========================
        if (user == null) {
            return "login";
        }
        model.addAttribute("user", user);
        GoodsVo goodsVo = goodsService.findGoodsVoByGoodsId(goodsId);
        //判断库存
        if (goodsVo.getStockCount() < 1) {
            model.addAttribute("errmsg", RespBeanEnum.ENTRY_STOCK.getMessage());
            return "secKillFail";
        }
        //解决重复抢购,直接到redis中获取对应的秒杀订单，如果有则说明已经抢购了，不能继续抢购
        SeckillOrder seckillOrder = (SeckillOrder) redisTemplate.opsForValue().get("order:" + user.getId() + ":" + goodsId);
        if (seckillOrder != null) {
            model.addAttribute("errmsg", RespBeanEnum.REPEATE_ERROR.getMessage());
            return "secKillFail";
        }

        //库存预减，如果在redis中预减库存，发现秒杀商品中已经没有库存了，直接返回
        //从而减少这个方法请求 orderService.seckill防止大量请求打到数据，优化秒杀
        //这个方法具有原子性！！！
        Long decrement = redisTemplate.opsForValue().decrement("seckillGoods:" + goodsId);
        //说明这个商品已经没有库存了
        if (decrement < 0) {
            //恢复redis库存为0,对业务没有影响只是为了好看
            redisTemplate.opsForValue().increment("seckillGoods:" + goodsId);
            model.addAttribute("errmsg", RespBeanEnum.REPEATE_ERROR.getMessage());
            return "secKillFail";
        }

        //抢购
        Order order = orderService.seckill(user, goodsVo);
        if (order == null) {
            model.addAttribute("errmsg", RespBeanEnum.ENTRY_STOCK.getMessage());
            return "secKillFail";
        }
        model.addAttribute("order", order);
        model.addAttribute("goods", goodsVo);
        return "orderDetail";
        //===================秒杀 v3.0 end... =========================
    }

    //该方法实在类的所有属性都初始化后，自动执行
    //这里将所有秒杀商品的库存量加载到redis中
    @Override
    public void afterPropertiesSet() throws Exception {
        //1.查询所有的秒杀商品
        List<GoodsVo> list = goodsService.findGoodsVo();
        if (CollectionUtils.isEmpty(list)) {
            return;
        }
        //遍历list,将秒杀商品的库存量放入到redis中
        //秒杀商品库存量对应的key seckillGoods:商品id
        for (GoodsVo goodsVo : list) {
            redisTemplate.opsForValue().set("seckillGoods:" + goodsVo.getId(), goodsVo.getStockCount());
        }
    }

}

@Controller
@RequestMapping(value = "/seckill")
public class SeckillController implements InitializingBean {

    @Resource
    private GoodsService goodsService;

    @Resource
    private SeckillOrderService seckillOrderService;

    @Resource
    private OrderService orderService;

    @Resource
    private RedisTemplate redisTemplate;

    @RequestMapping(value = "/doSeckill")
    public String doSeckill(Model model, User user, Long goodsId) {
        System.out.println("-----秒杀 V3.0--------");
        //===================秒杀 v3.0 start =========================
        if (user == null) {
            return "login";
        }
        model.addAttribute("user", user);
        GoodsVo goodsVo = goodsService.findGoodsVoByGoodsId(goodsId);
        //判断库存
        if (goodsVo.getStockCount() < 1) {
            model.addAttribute("errmsg", RespBeanEnum.ENTRY_STOCK.getMessage());
            return "secKillFail";
        }
        //解决重复抢购,直接到redis中获取对应的秒杀订单，如果有则说明已经抢购了，不能继续抢购
        SeckillOrder seckillOrder = (SeckillOrder) redisTemplate.opsForValue().get("order:" + user.getId() + ":" + goodsId);
        if (seckillOrder != null) {
            model.addAttribute("errmsg", RespBeanEnum.REPEATE_ERROR.getMessage());
            return "secKillFail";
        }

        //库存预减，如果在redis中预减库存，发现秒杀商品中已经没有库存了，直接返回
        //从而减少这个方法请求 orderService.seckill防止大量请求打到数据，优化秒杀
        //这个方法具有原子性！！！
        Long decrement = redisTemplate.opsForValue().decrement("seckillGoods:" + goodsId);
        //说明这个商品已经没有库存了
        if (decrement < 0) {
            //恢复redis库存为0,对业务没有影响只是为了好看
            redisTemplate.opsForValue().increment("seckillGoods:" + goodsId);
            model.addAttribute("errmsg", RespBeanEnum.REPEATE_ERROR.getMessage());
            return "secKillFail";
        }

        //抢购
        Order order = orderService.seckill(user, goodsVo);
        if (order == null) {
            model.addAttribute("errmsg", RespBeanEnum.ENTRY_STOCK.getMessage());
            return "secKillFail";
        }
        model.addAttribute("order", order);
        model.addAttribute("goods", goodsVo);
        return "orderDetail";
        //===================秒杀 v3.0 end... =========================
    }

    //该方法实在类的所有属性都初始化后，自动执行
    //这里将所有秒杀商品的库存量加载到redis中
    @Override
    public void afterPropertiesSet() throws Exception {
        //1.查询所有的秒杀商品
        List<GoodsVo> list = goodsService.findGoodsVo();
        if (CollectionUtils.isEmpty(list)) {
            return;
        }
        //遍历list,将秒杀商品的库存量放入到redis中
        //秒杀商品库存量对应的key seckillGoods:商品id
        for (GoodsVo goodsVo : list) {
            redisTemplate.opsForValue().set("seckillGoods:" + goodsVo.getId(), goodsVo.getStockCount());
        }
    }

}

大体思路：

项目启动时加载秒杀商品库存到redis中，库存量随着每次启动都会更新
在进行抢购之前先到redis中进行库存预减，利用redis的decrement具备原子性的特点
如果redis预减库存小于0则直接返回，避免了多余的请求打到数据库

3.4 v4.0 优化秒杀：加入内存标记，避免总到 Reids 查询库存

需求分析/图解

如果某个商品库存已经为空了, 我们仍然是到 Redis 去查询的, 还可以进行优化
解决方案: 给商品进行内存标记, 如果库存为空, 直接返回, 避免总是到 Redis 查询库存
分析思路-示意图

java

@Controller
@RequestMapping(value = "/seckill")
public class SeckillController implements InitializingBean {

    @Resource
    private GoodsService goodsService;

    @Resource
    private SeckillOrderService seckillOrderService;

    @Resource
    private OrderService orderService;

    @Resource
    private RedisTemplate redisTemplate;

    @RequestMapping(value = "/doSeckill")
    public String doSeckill(Model model, User user, Long goodsId) {
        System.out.println("-----秒杀 V4.0--------");
        //===================秒杀 v4.0 start =========================
        if (user == null) {
            return "login";
        }
        model.addAttribute("user", user);
        GoodsVo goodsVo = goodsService.findGoodsVoByGoodsId(goodsId);
        //判断库存
        if (goodsVo.getStockCount() < 1) {
            model.addAttribute("errmsg", RespBeanEnum.ENTRY_STOCK.getMessage());
            return "secKillFail";
        }
        //解决重复抢购,直接到redis中获取对应的秒杀订单，如果有则说明已经抢购了，不能继续抢购
        SeckillOrder seckillOrder = (SeckillOrder) redisTemplate.opsForValue().get("order:" + user.getId() + ":" + goodsId);
        if (seckillOrder != null) {
            model.addAttribute("errmsg", RespBeanEnum.REPEATE_ERROR.getMessage());
            return "secKillFail";
        }

        //如果库存为空，避免总是到 reids 去查询库存，给 redis 增加负担（内存标记）
        if (entryStockMap.get(goodsId)) {
            //如果当前这个秒杀商品已经是空库存，则直接返回.
            model.addAttribute("errmsg", RespBeanEnum.ENTRY_STOCK.getMessage());
            return "secKillFail";
        }

        //库存预减，如果在redis中预减库存，发现秒杀商品中已经没有库存了，直接返回
        //从而减少这个方法请求 orderService.seckill防止大量请求打到数据，优化秒杀
        //这个方法具有原子性！！！
        Long decrement = redisTemplate.opsForValue().decrement("seckillGoods:" + goodsId);
        //说明这个商品已经没有库存了
        if (decrement < 0) {
            //这里使用内存标记，避免多次操作 redis, true 表示空库存了.
            entryStockMap.put(goodsId, true);
            //恢复redis库存为0,对业务没有影响只是为了好看
            redisTemplate.opsForValue().increment("seckillGoods:" + goodsId);
            model.addAttribute("errmsg", RespBeanEnum.REPEATE_ERROR.getMessage());
            return "secKillFail";
        }

        //抢购
        Order order = orderService.seckill(user, goodsVo);
        if (order == null) {
            model.addAttribute("errmsg", RespBeanEnum.ENTRY_STOCK.getMessage());
            return "secKillFail";
        }
        model.addAttribute("order", order);
        model.addAttribute("goods", goodsVo);
        return "orderDetail";
        //===================秒杀 v4.0 end... =========================
    }

    //该方法实在类的所有属性都初始化后，自动执行
    //这里将所有秒杀商品的库存量加载到redis中
    @Override
    public void afterPropertiesSet() throws Exception {
        //1.查询所有的秒杀商品
        List<GoodsVo> list = goodsService.findGoodsVo();
        if (CollectionUtils.isEmpty(list)) {
            return;
        }
        //遍历list,将秒杀商品的库存量放入到redis中
        //秒杀商品库存量对应的key seckillGoods:商品id
        for (GoodsVo goodsVo : list) {
            redisTemplate.opsForValue().set("seckillGoods:" + goodsVo.getId(), goodsVo.getStockCount());
            //当有库存为 false，当无库存为 true。防止库存没有了，还会到 Redis 进行判断操作
            entryStockMap.put(goodsVo.getId(), false);
        }
    }

}

@Controller
@RequestMapping(value = "/seckill")
public class SeckillController implements InitializingBean {

    @Resource
    private GoodsService goodsService;

    @Resource
    private SeckillOrderService seckillOrderService;

    @Resource
    private OrderService orderService;

    @Resource
    private RedisTemplate redisTemplate;

    @RequestMapping(value = "/doSeckill")
    public String doSeckill(Model model, User user, Long goodsId) {
        System.out.println("-----秒杀 V4.0--------");
        //===================秒杀 v4.0 start =========================
        if (user == null) {
            return "login";
        }
        model.addAttribute("user", user);
        GoodsVo goodsVo = goodsService.findGoodsVoByGoodsId(goodsId);
        //判断库存
        if (goodsVo.getStockCount() < 1) {
            model.addAttribute("errmsg", RespBeanEnum.ENTRY_STOCK.getMessage());
            return "secKillFail";
        }
        //解决重复抢购,直接到redis中获取对应的秒杀订单，如果有则说明已经抢购了，不能继续抢购
        SeckillOrder seckillOrder = (SeckillOrder) redisTemplate.opsForValue().get("order:" + user.getId() + ":" + goodsId);
        if (seckillOrder != null) {
            model.addAttribute("errmsg", RespBeanEnum.REPEATE_ERROR.getMessage());
            return "secKillFail";
        }

        //如果库存为空，避免总是到 reids 去查询库存，给 redis 增加负担（内存标记）
        if (entryStockMap.get(goodsId)) {
            //如果当前这个秒杀商品已经是空库存，则直接返回.
            model.addAttribute("errmsg", RespBeanEnum.ENTRY_STOCK.getMessage());
            return "secKillFail";
        }

        //库存预减，如果在redis中预减库存，发现秒杀商品中已经没有库存了，直接返回
        //从而减少这个方法请求 orderService.seckill防止大量请求打到数据，优化秒杀
        //这个方法具有原子性！！！
        Long decrement = redisTemplate.opsForValue().decrement("seckillGoods:" + goodsId);
        //说明这个商品已经没有库存了
        if (decrement < 0) {
            //这里使用内存标记，避免多次操作 redis, true 表示空库存了.
            entryStockMap.put(goodsId, true);
            //恢复redis库存为0,对业务没有影响只是为了好看
            redisTemplate.opsForValue().increment("seckillGoods:" + goodsId);
            model.addAttribute("errmsg", RespBeanEnum.REPEATE_ERROR.getMessage());
            return "secKillFail";
        }

        //抢购
        Order order = orderService.seckill(user, goodsVo);
        if (order == null) {
            model.addAttribute("errmsg", RespBeanEnum.ENTRY_STOCK.getMessage());
            return "secKillFail";
        }
        model.addAttribute("order", order);
        model.addAttribute("goods", goodsVo);
        return "orderDetail";
        //===================秒杀 v4.0 end... =========================
    }

    //该方法实在类的所有属性都初始化后，自动执行
    //这里将所有秒杀商品的库存量加载到redis中
    @Override
    public void afterPropertiesSet() throws Exception {
        //1.查询所有的秒杀商品
        List<GoodsVo> list = goodsService.findGoodsVo();
        if (CollectionUtils.isEmpty(list)) {
            return;
        }
        //遍历list,将秒杀商品的库存量放入到redis中
        //秒杀商品库存量对应的key seckillGoods:商品id
        for (GoodsVo goodsVo : list) {
            redisTemplate.opsForValue().set("seckillGoods:" + goodsVo.getId(), goodsVo.getStockCount());
            //当有库存为 false，当无库存为 true。防止库存没有了，还会到 Redis 进行判断操作
            entryStockMap.put(goodsVo.getId(), false);
        }
    }

}

3.4 v5.0 优化秒杀: 加入消息队列，实现秒杀的异步请求

需求分析/图解

问题分析

前面秒杀, 没有实现异步机制, 是完成下订单后, 再返回的, 当有大并发请求下订单操作时, 数据库来不及响应, 容易造成线程堆积

解决方案

加入消息队列，实现秒杀的异步请求
接收到客户端秒杀请求后，服务器立即返回正在秒杀中.., 有利于流量削峰
客户端进行轮询秒杀结果, 接收到秒杀结果后，在客户端页面显示即可
秒杀消息发送设计 SeckillMessage - String

代码实现

秒杀消息类

java

@Data
@NoArgsConstructor
@AllArgsConstructor
public class SeckillMessage {
    private User user;
    private Long goodsId;
}

@Data
@NoArgsConstructor
@AllArgsConstructor
public class SeckillMessage {
    private User user;
    private Long goodsId;
}

定义消息队列、交换机

java

@Configuration
public class RabbitMQSecKillConfig {
    private static final String QUEUE = "seckillQueue";
    private static final String EXCHANGE = "seckillExchange";

    @Bean
    public Queue queue_seckill() {
        return new Queue(QUEUE);
    }

    @Bean
    public TopicExchange topicExchange_seckill() {
        return new TopicExchange(EXCHANGE);
    }

    @Bean
    public Binding binding_seckill() {
        return BindingBuilder.bind(queue_seckill())
                .to(topicExchange_seckill()).with("seckill.#");
    }

}

@Configuration
public class RabbitMQSecKillConfig {
    private static final String QUEUE = "seckillQueue";
    private static final String EXCHANGE = "seckillExchange";

    @Bean
    public Queue queue_seckill() {
        return new Queue(QUEUE);
    }

    @Bean
    public TopicExchange topicExchange_seckill() {
        return new TopicExchange(EXCHANGE);
    }

    @Bean
    public Binding binding_seckill() {
        return BindingBuilder.bind(queue_seckill())
                .to(topicExchange_seckill()).with("seckill.#");
    }

}

发送秒杀消息

java

@Service
@Slf4j
public class MQSenderMessage {

    @Resource
    private RabbitTemplate rabbitTemplate;

    //发送秒杀信息
    public void senderMessage(String message) {
        System.out.println("发送消息了=" + message);
        log.info("发送消息：" + message);
        rabbitTemplate.convertAndSend("seckillExchange", "seckill.message", message);
    }
}

@Service
@Slf4j
public class MQSenderMessage {

    @Resource
    private RabbitTemplate rabbitTemplate;

    //发送秒杀信息
    public void senderMessage(String message) {
        System.out.println("发送消息了=" + message);
        log.info("发送消息：" + message);
        rabbitTemplate.convertAndSend("seckillExchange", "seckill.message", message);
    }
}

消息接收者

java

@Service
@Slf4j
public class MQReceiverConsumer {

    @Resource
    private GoodsService goodsService;
    
    @Resource
    private OrderService orderService;

    //下单操作
    @RabbitListener(queues = "seckillQueue")
    public void queue(String message) {
        SeckillMessage seckillMessage = JSONUtil.toBean(message, SeckillMessage.class);
        Long goodId = seckillMessage.getGoodsId();
        User user = seckillMessage.getUser();
        //获取抢购的商品信息
        GoodsVo goodsVo = goodsService.findGoodsVoByGoodsId(goodId);
        //下单操作
        orderService.seckill(user, goodsVo);
    }

}

@Service
@Slf4j
public class MQReceiverConsumer {

    @Resource
    private GoodsService goodsService;
    
    @Resource
    private OrderService orderService;

    //下单操作
    @RabbitListener(queues = "seckillQueue")
    public void queue(String message) {
        SeckillMessage seckillMessage = JSONUtil.toBean(message, SeckillMessage.class);
        Long goodId = seckillMessage.getGoodsId();
        User user = seckillMessage.getUser();
        //获取抢购的商品信息
        GoodsVo goodsVo = goodsService.findGoodsVoByGoodsId(goodId);
        //下单操作
        orderService.seckill(user, goodsVo);
    }

}

SeckillController

java

@Controller
@RequestMapping(value = "/seckill")
public class SeckillController implements InitializingBean {

    @Resource
    private GoodsService goodsService;

    @Resource
    private RedisTemplate redisTemplate;

    @Resource
    private MQSenderMessage mqSenderMessage;

    //如果某个商品库存已经为空, 则标记到 entryStockMap
    private HashMap<Long, Boolean> entryStockMap = new HashMap<>();

    @RequestMapping(value = "/doSeckill")
    public String doSeckill(Model model, User user, Long goodsId) {
        System.out.println("-----秒杀 V5.0--------");
        //===================秒杀 v5.0 start =========================
        if (user == null) {
            return "login";
        }
        model.addAttribute("user", user);
        GoodsVo goodsVo = goodsService.findGoodsVoByGoodsId(goodsId);
        //判断库存
        if (goodsVo.getStockCount() < 1) {
            model.addAttribute("errmsg", RespBeanEnum.ENTRY_STOCK.getMessage());
            return "secKillFail";
        }
        //解决重复抢购,直接到redis中获取对应的秒杀订单，如果有则说明已经抢购了，不能继续抢购
        SeckillOrder seckillOrder = (SeckillOrder) redisTemplate.opsForValue().get("order:" + user.getId() + ":" + goodsId);
        if (seckillOrder != null) {
            model.addAttribute("errmsg", RespBeanEnum.REPEATE_ERROR.getMessage());
            return "secKillFail";
        }

        //如果库存为空，避免总是到 reids 去查询库存，给 redis 增加负担（内存标记）
        if (entryStockMap.get(goodsId)) {
            //如果当前这个秒杀商品已经是空库存，则直接返回.
            model.addAttribute("errmsg", RespBeanEnum.ENTRY_STOCK.getMessage());
            return "secKillFail";
        }

        //库存预减，如果在redis中预减库存，发现秒杀商品中已经没有库存了，直接返回
        //从而减少这个方法请求 orderService.seckill防止大量请求打到数据，优化秒杀
        //这个方法具有原子性！！！
        Long decrement = redisTemplate.opsForValue().decrement("seckillGoods:" + goodsId);
        //说明这个商品已经没有库存了
        if (decrement < 0) {
            //这里使用内存标记，避免多次操作 redis, true 表示空库存了.
            entryStockMap.put(goodsId, true);
            //恢复redis库存为0,对业务没有影响只是为了好看
            redisTemplate.opsForValue().increment("seckillGoods:" + goodsId);
            model.addAttribute("errmsg", RespBeanEnum.REPEATE_ERROR.getMessage());
            return "secKillFail";
        }

        //抢购
        // Order order = orderService.seckill(user, goodsVo);
        // if (order == null) {
        //     model.addAttribute("errmsg", RespBeanEnum.ENTRY_STOCK.getMessage());
        //     return "secKillFail";
        // }
        // model.addAttribute("order", order);
        // model.addAttribute("goods", goodsVo);
        //抢购, 向 MQ 发消息, 因为不知道是否成功, 客户端需要轮询
        //errmsg 为排队中.... , 暂时返回 "secKillFaill" 页面
        SeckillMessage seckillMessage =
                new SeckillMessage(user, goodsId);
        mqSenderMessage.senderMessage
                (JSONUtil.toJsonStr(seckillMessage));
        model.addAttribute("errmsg", "排队中.....");
        return "orderDetail";
        //===================秒杀 v5.0 end... =========================
    }


    //该方法实在类的所有属性都初始化后，自动执行
    //这里将所有秒杀商品的库存量加载到redis中
    @Override
    public void afterPropertiesSet() throws Exception {
        //1.查询所有的秒杀商品
        List<GoodsVo> list = goodsService.findGoodsVo();
        if (CollectionUtils.isEmpty(list)) {
            return;
        }
        //遍历list,将秒杀商品的库存量放入到redis中
        //秒杀商品库存量对应的key seckillGoods:商品id
        for (GoodsVo goodsVo : list) {
            redisTemplate.opsForValue().set("seckillGoods:" + goodsVo.getId(), goodsVo.getStockCount());
            //当有库存为 false，当无库存为 true。防止库存没有了，还会到 Redis 进行判断操作
            entryStockMap.put(goodsVo.getId(), false);
        }
    }

}

@Controller
@RequestMapping(value = "/seckill")
public class SeckillController implements InitializingBean {

    @Resource
    private GoodsService goodsService;

    @Resource
    private RedisTemplate redisTemplate;

    @Resource
    private MQSenderMessage mqSenderMessage;

    //如果某个商品库存已经为空, 则标记到 entryStockMap
    private HashMap<Long, Boolean> entryStockMap = new HashMap<>();

    @RequestMapping(value = "/doSeckill")
    public String doSeckill(Model model, User user, Long goodsId) {
        System.out.println("-----秒杀 V5.0--------");
        //===================秒杀 v5.0 start =========================
        if (user == null) {
            return "login";
        }
        model.addAttribute("user", user);
        GoodsVo goodsVo = goodsService.findGoodsVoByGoodsId(goodsId);
        //判断库存
        if (goodsVo.getStockCount() < 1) {
            model.addAttribute("errmsg", RespBeanEnum.ENTRY_STOCK.getMessage());
            return "secKillFail";
        }
        //解决重复抢购,直接到redis中获取对应的秒杀订单，如果有则说明已经抢购了，不能继续抢购
        SeckillOrder seckillOrder = (SeckillOrder) redisTemplate.opsForValue().get("order:" + user.getId() + ":" + goodsId);
        if (seckillOrder != null) {
            model.addAttribute("errmsg", RespBeanEnum.REPEATE_ERROR.getMessage());
            return "secKillFail";
        }

        //如果库存为空，避免总是到 reids 去查询库存，给 redis 增加负担（内存标记）
        if (entryStockMap.get(goodsId)) {
            //如果当前这个秒杀商品已经是空库存，则直接返回.
            model.addAttribute("errmsg", RespBeanEnum.ENTRY_STOCK.getMessage());
            return "secKillFail";
        }

        //库存预减，如果在redis中预减库存，发现秒杀商品中已经没有库存了，直接返回
        //从而减少这个方法请求 orderService.seckill防止大量请求打到数据，优化秒杀
        //这个方法具有原子性！！！
        Long decrement = redisTemplate.opsForValue().decrement("seckillGoods:" + goodsId);
        //说明这个商品已经没有库存了
        if (decrement < 0) {
            //这里使用内存标记，避免多次操作 redis, true 表示空库存了.
            entryStockMap.put(goodsId, true);
            //恢复redis库存为0,对业务没有影响只是为了好看
            redisTemplate.opsForValue().increment("seckillGoods:" + goodsId);
            model.addAttribute("errmsg", RespBeanEnum.REPEATE_ERROR.getMessage());
            return "secKillFail";
        }

        //抢购
        // Order order = orderService.seckill(user, goodsVo);
        // if (order == null) {
        //     model.addAttribute("errmsg", RespBeanEnum.ENTRY_STOCK.getMessage());
        //     return "secKillFail";
        // }
        // model.addAttribute("order", order);
        // model.addAttribute("goods", goodsVo);
        //抢购, 向 MQ 发消息, 因为不知道是否成功, 客户端需要轮询
        //errmsg 为排队中.... , 暂时返回 "secKillFaill" 页面
        SeckillMessage seckillMessage =
                new SeckillMessage(user, goodsId);
        mqSenderMessage.senderMessage
                (JSONUtil.toJsonStr(seckillMessage));
        model.addAttribute("errmsg", "排队中.....");
        return "orderDetail";
        //===================秒杀 v5.0 end... =========================
    }


    //该方法实在类的所有属性都初始化后，自动执行
    //这里将所有秒杀商品的库存量加载到redis中
    @Override
    public void afterPropertiesSet() throws Exception {
        //1.查询所有的秒杀商品
        List<GoodsVo> list = goodsService.findGoodsVo();
        if (CollectionUtils.isEmpty(list)) {
            return;
        }
        //遍历list,将秒杀商品的库存量放入到redis中
        //秒杀商品库存量对应的key seckillGoods:商品id
        for (GoodsVo goodsVo : list) {
            redisTemplate.opsForValue().set("seckillGoods:" + goodsVo.getId(), goodsVo.getStockCount());
            //当有库存为 false，当无库存为 true。防止库存没有了，还会到 Redis 进行判断操作
            entryStockMap.put(goodsVo.getId(), false);
        }
    }

}

客户端轮询秒杀结果-思路分析示意图

秒杀高并发解决方案 ​

1.秒杀/高并发方案-介绍 ​

2.秒杀场景模拟 ​

3.秒杀解决方案 ​

3.1 v1.0-原始版本 ​

3.2 v2.0-秒杀-复购、超卖处理 ​

3.3 v3.0 优化秒杀，Redis 预减库存 ​

3.4 v4.0 优化秒杀：加入内存标记，避免总到 Reids 查询库存 ​

3.4 v5.0 优化秒杀: 加入消息队列，实现秒杀的异步请求 ​

秒杀高并发解决方案

1.秒杀/高并发方案-介绍

2.秒杀场景模拟

3.秒杀解决方案

3.1 v1.0-原始版本

3.2 v2.0-秒杀-复购、超卖处理

3.3 v3.0 优化秒杀，Redis 预减库存

3.4 v4.0 优化秒杀：加入内存标记，避免总到 Reids 查询库存

3.4 v5.0 优化秒杀: 加入消息队列，实现秒杀的异步请求