@Service
public class ProductService {
    @Resource
    private ProductMapper productMapper;
    @Resource
    private StringRedisTemplate redisTemplate;
    @Resource
    private CacheDeleteProducer cacheDeleteProducer;
    @Transactional(rollbackFor = Exception.class)
    public void updateProduct(Product product) {
        String key = "product:" + product.getId();
        // 1) 數(shù)據(jù)庫是事實來源
        productMapper.updateById(product);
        // 2) 主流程刪緩存，失敗則入重試隊列
        try {
            redisTemplate.delete(key);
        } catch (Exception ex) {
            cacheDeleteProducer.sendDeleteEvent(key, 1);
        }
    }
}

@Component
public class CacheDeleteConsumer {
    private static final int MAX_RETRY = 5;
    @Resource
    private StringRedisTemplate redisTemplate;
    @Resource
    private CacheDeleteProducer cacheDeleteProducer;
    @Resource
    private DeadLetterProducer deadLetterProducer;
    public void onMessage(CacheDeleteEvent event) {
        try {
            redisTemplate.delete(event.getCacheKey());
            // 打點：delete_success_total +1
        } catch (Exception ex) {
            int nextRetry = event.getRetryCount() + 1;
            if (nextRetry > MAX_RETRY) {
                deadLetterProducer.send(event.getCacheKey(), ex.getMessage());
                return;
            }
            long delaySeconds = (long) Math.pow(2, nextRetry); // 2,4,8,16,32
            cacheDeleteProducer.sendDeleteEvent(event.getCacheKey(), nextRetry, delaySeconds);
        }
    }
}

@Component
public class CacheDeleteCompensationJob {
    @Resource
    private DeadLetterRepository deadLetterRepository;
    @Resource
    private StringRedisTemplate redisTemplate;
    // 每 5 分鐘跑一次
    @Scheduled(cron = "0 */5 * * * ?")
    public void compensate() {
        List<DeadLetterRecord> records = deadLetterRepository.queryUnresolved(200);
        for (DeadLetterRecord record : records) {
            try {
                redisTemplate.delete(record.getCacheKey());
                deadLetterRepository.markResolved(record.getId());
            } catch (Exception e) {
                deadLetterRepository.increaseFailCount(record.getId(), e.getMessage());
            }
        }
    }
}