CREATE DATABASE `SEQID`;

CREATE TABLE SEQID.SEQUENCE_ID (
	id bigint(20) unsigned NOT NULL auto_increment, 
	stub char(10) NOT NULL default '',
	PRIMARY KEY (id),
	UNIQUE KEY stub (stub)
) ENGINE=MyISAM;

begin;
replace into SEQUENCE_ID (stub) VALUES ('anyword');
select last_insert_id();
commit;

set @@auto_increment_offset = 1;     -- 起始值
set @@auto_increment_increment = 2;  -- 步长

set @@auto_increment_offset = 2;     -- 起始值
set @@auto_increment_increment = 2;  -- 步长

CREATE TABLE id_generator (
  id int(10) NOT NULL,
  current_max_id bigint(20) NOT NULL COMMENT '当前最大id',
  increment_step int(10) NOT NULL COMMENT '自增步长',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

update id_generator set current_max_id=#{newMaxId}, version=version+1 where version = #{version}

package com.yeming.tinyid.application;

import static java.lang.System.*;

/**
 * @author yeming.gao
 * @Description: 雪花算法实现
 * p>
 * SnowFlake算法用来生成64位的ID，刚好可以用long整型存储，能够用于分布式系统中生产唯一的ID，
 * 并且生成的ID有大致的顺序。 在这次实现中，生成的64位ID可以分成5个部分：
 * 0 - 41位时间戳 - 5位数据中心标识 - 5位机器标识 - 12位序列号
 * @date 2020/07/28 16:15
 */
public class SnowFlake {
    /**
     * 起始的时间戳
     */
    private static final long START_STMP = 1480166465631L;

    /**
     * 机器标识占用的位数
     */
    private static final long MACHINE_BIT = 5;
    /**
     * 数据中心占用的位数
     */
    private static final long DATACENTER_BIT = 5;
    /**
     * 序列号占用的位数
     */
    private static final long SEQUENCE_BIT = 12;

    /**
     * 机器标识最大值
     */
    private static final long MAX_MACHINE_NUM = ~(-1L  MACHINE_BIT);
    /**
     * 数据中心最大值
     */
    private static final long MAX_DATACENTER_NUM = ~(-1L  DATACENTER_BIT);
    /**
     * 序列号最大值
     */
    private static final long MAX_SEQUENCE = ~(-1L  SEQUENCE_BIT);
    /**
     * 每一部分向左的位移
     */
    private static final long MACHINE_LEFT = SEQUENCE_BIT;
    private static final long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private static final long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

    private long datacenterId; //数据中心
    private long machineId; //机器标识
    private long sequence = 0L; //序列号
    private long lastStmp = -1L;//上一次时间戳

    private SnowFlake(long datacenterId, long machineId) {
        if (datacenterId > MAX_DATACENTER_NUM || datacenterId  0) {
            throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId  0) {
            throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
        }
        this.datacenterId = datacenterId;
        this.machineId = machineId;
    }

    /**
     * 产生下一个ID
     *
     * @return long
     */
    private synchronized long nextId() {
        long currStmp = System.currentTimeMillis();
        if (currStmp  lastStmp) {
            throw new RuntimeException("Clock moved backwards. Refusing to generate id");
        }
        if (currStmp == lastStmp) {
            //相同毫秒内，序列号自增
            sequence = (sequence + 1)  MAX_SEQUENCE;
            //同一毫秒的序列数已经达到最大
            if (sequence == 0L) {
                currStmp = getNextMill();
            }
        } else {
            //不同毫秒内，序列号置为0
            sequence = 0L;
        }
        lastStmp = currStmp;
        return (currStmp - START_STMP)  TIMESTMP_LEFT //时间戳部分
                | datacenterId  DATACENTER_LEFT //数据中心部分
                | machineId  MACHINE_LEFT //机器标识部分
                | sequence; //序列号部分
    }

    private long getNextMill() {
        long mill = System.currentTimeMillis();
        while (mill = lastStmp) {
            mill = System.currentTimeMillis();
        }
        return mill;
    }

    public static void main(String[] args) {
        SnowFlake snowFlake = new SnowFlake(2, 3);
        //数据中心标识最大值
        long maxDatacenterNum = ~(-1L  DATACENTER_BIT);
        //机器标识最大值
        long maxMachineNum = ~(-1L  MACHINE_BIT);
        //序列号最大值
        long maxSequence = ~(-1L  SEQUENCE_BIT);
        out.println("数据中心标识最大值:" + maxDatacenterNum + ";机器标识最大值:" + maxMachineNum + ";序列号最大值:" + maxSequence);
        for (int i = 0; i  (1  12); i++) {
            out.println(snowFlake.nextId());
        }
    }
}