线上订单号重复了？一招搞定它！

短命女 2023-07-24 08:22 6阅读 0赞

## 问题的背景 ##

公司老的系统原先采用的时间戳生成订单号，导致了如下情形  
![在这里插入图片描述][20200410102625923.png]  
![在这里插入图片描述][20200410102653920.gif_pic_center]  
打断一下：大家知道怎么查系统某项重复的数据吧  
`SELECT * FROM XX表 WHERE 重复项 in( SELECT 重复项 FROM XX表 GROUP BY 重复项 HAVING count(1) >= 2)`

## 解决方法 ##

**不得了，这样重复岂不是一单成功三方回调导致另一单也成功了。**

多个服务怎么保证生成的订单号唯一呢？

先上code

package com.zhongjian.util;
    
    public class IdWorkerUtil{ 
    
        private long workerId;
        private long datacenterId;
        private long sequence;
    
        public IdWorkerUtil(long workerId, long datacenterId, long sequence){ 
            // sanity check for workerId
            if (workerId > maxWorkerId || workerId < 0) { 
                throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0",maxWorkerId));
            }
            if (datacenterId > maxDatacenterId || datacenterId < 0) { 
                throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0",maxDatacenterId));
            }
            System.out.printf("worker starting. timestamp left shift %d, datacenter id bits %d, worker id bits %d, sequence bits %d, workerid %d",
                    timestampLeftShift, datacenterIdBits, workerIdBits, sequenceBits, workerId);
    
            this.workerId = workerId;
            this.datacenterId = datacenterId;
            this.sequence = sequence;
        }
    
        private long twepoch = 1288834974657L;
    
        private long workerIdBits = 5L;
        private long datacenterIdBits = 5L;
        private long maxWorkerId = -1L ^ (-1L << workerIdBits);
        private long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
        private long sequenceBits = 12L;
    
        private long workerIdShift = sequenceBits;
        private long datacenterIdShift = sequenceBits + workerIdBits;
        private long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
        private long sequenceMask = -1L ^ (-1L << sequenceBits);
    
        private long lastTimestamp = -1L;
    
        public long getWorkerId(){ 
            return workerId;
        }
    
        public long getDatacenterId(){ 
            return datacenterId;
        }
    
        public long getTimestamp(){ 
            return System.currentTimeMillis();
        }
    
        public synchronized long nextId() { 
            long timestamp = timeGen();
    
            if (timestamp < lastTimestamp) { 
                System.err.printf("clock is moving backwards. Rejecting requests until %d.", lastTimestamp);
                throw new RuntimeException(String.format("Clock moved backwards. Refusing to generate id for %d milliseconds",
                        lastTimestamp - timestamp));
            }
    
            if (lastTimestamp == timestamp) { 
                sequence = (sequence + 1) & sequenceMask;
                if (sequence == 0) { 
                    timestamp = tilNextMillis(lastTimestamp);
                }
            } else { 
                sequence = 0;
            }
    
            lastTimestamp = timestamp;
            return ((timestamp - twepoch) << timestampLeftShift) |
                    (datacenterId << datacenterIdShift) |
                    (workerId << workerIdShift) |
                    sequence;
        }
    
        private long tilNextMillis(long lastTimestamp) { 
            long timestamp = timeGen();
            while (timestamp <= lastTimestamp) { 
                timestamp = timeGen();
            }
            return timestamp;
        }
    
        private long timeGen(){ 
            return System.currentTimeMillis();
        }
    
        public static void main(String[] args) { 
            IdWorkerUtil idWorkerUtil = new IdWorkerUtil(1,1,0L);
            System.out.println(idWorkerUtil.nextId());
        }
    
    }

<table> 
 <thead> 
  <tr> 
   <th>位</th> 
   <th>Value</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>第1位</td> 
   <td>0</td> 
  </tr> 
  <tr> 
   <td>第2-42位</td> 
   <td>毫秒级时间41位的长度可以使用69年</td> 
  </tr> 
  <tr> 
   <td>第43-52位</td> 
   <td>5位datacenterId和5位workerId10位的长度最多支持部署1024个节点</td> 
  </tr> 
  <tr> 
   <td>第53-64位</td> 
   <td>毫秒内的计数12位的计数顺序号支持每个节点每毫秒产生4096个ID序号</td> 
  </tr> 
 </tbody> 
</table>

以上是采用snowflake算法生成分布式唯一ID

**41-bit的时间可以表示（1L<<41）/(1000L*3600*24\*365)=69年的时间，10-bit机器可以分别表示1024台机器。如果我们对IDC划分有需求，还可以将10-bit分5-bit给IDC，分5-bit给工作机器。这样就可以表示32个IDC，每个IDC下可以有32台机器，可以根据自身需求定义。12个自增序列号可以表示2^12个ID，理论上snowflake方案的QPS约为409.6w/s，这种分配方式可以保证在任何一个IDC的任何一台机器在任意毫秒内生成的ID都是不同的。**

这种方式的优缺点是：

优点：  
**1、毫秒数在高位，自增序列在低位，整个ID都是趋势递增的。  
2、不依赖数据库等第三方系统，以服务的方式部署，稳定性更高，生成ID的性能也是非常高的。  
3、’可以根据自身业务特性分配bit位，非常灵活。**

缺点：  
**强依赖机器时钟，如果机器上时钟回拨，会导致发号重复或者服务会处于不可用状态。**

一般来说，采用这种方案就解决了。

**还有诸如，mysql的 auto\_increment策略，redis的INCR，zookeeper的单一节点修改版本号递增，以及zookeeper的持久顺序节点。**

看完点个赞呗~

参考

https://tech.meituan.com/2017/04/21/mt-leaf.html  
https://www.cnblogs.com/qianzhengkai/p/11151613.html

[20200410102625923.png]: /images/20230528/788b76e663784b45b1d474e0cd9b85d7.png
[20200410102653920.gif_pic_center]: /images/20230528/e62fbd8d31044a9e9c4f5549ac01311f.png