Twitter开源分布式自增ID算法snowflake

分布式唯一ID

一、UUID

优点

* 生成ID性能非常好

* 简单，代码方便

* 全球唯一

缺点

*  uuid没有顺序，不能保证自增

* 太长，使用字符串存储，作为主键建立索引查询效率低

二、snowflake 雪花算法

18位 数字

算法：通过时间戳 + 机器码 + 序列码

数据库用 bigint 只占8个字节

代码：

public class IdWorker {
    //protected static final Logger LOG = LoggerFactory.getLogger(IdWorker.class);
    
    private long workerId;
    private long datacenterId;
    private long sequence = 0L;
 
    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 IdWorker(long workerId, long datacenterId) {
        // 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));
        }
        this.workerId = workerId;
        this.datacenterId = datacenterId;
       // LOG.info(String.format("worker starting. timestamp left shift %d, datacenter id bits %d, worker id bits %d, sequence bits %d, workerid %d", timestampLeftShift, datacenterIdBits, workerIdBits, sequenceBits, workerId));
    }
 
    public synchronized long nextId() {
        long timestamp = timeGen();
 
        if (timestamp < lastTimestamp) {
           // LOG.error(String.format("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 = 0L;
        }
 
        lastTimestamp = timestamp;
 
        return ((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence;
    }
 
    protected long tilNextMillis(long lastTimestamp) {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = timeGen();
        }
        return timestamp;
    }
 
    protected long timeGen() {
        return System.currentTimeMillis();
    }
}

调用

IdWorker idWorker1 = new IdWorker(1,0);
            
            for (int i = 0; i < 20; i++) {
                long id = idWorker1.nextId();
                System.out.println(id);
        }