雪花算法生成全局Id，看这篇就够了

news2024/10/6 1:37:56

分布式id

雪花算法能够生成一个64位long类型数据，适合做分布式系统的全局标识符，或者分库分表中，同类型数据表的主键

原理探究

雪花算法：以一台服务器为对象，在一毫秒时间内，生成一个自增的long数据
特点：雪花算法生成的id具有唯一性，和实时性

下面，就来研究一下，雪花id是如何保证全局唯一的

组成

划重点：一位符号位，41位时间毫秒数，10位机器id，12位同毫秒自增序号，共64位
在这里插入图片描述
由此，我们可以分析得出以下结论：

时间戳位于高位，且时间戳随时间递增，所以，雪花id随时间递增
10位机器id，一共可以为2^10=1024台服务器生成id
12位序列号，即在1毫秒内，可以生成2^12=4096个id，换句话说，就是雪花id最高支持409 万的每秒并发量
雪花id是否会重复，取决于时间戳是否重复，也就是说，当服务器调回过去的时间时，就会导致雪花id不再唯一

生成过程

/**
 * 雪花算法生成id
 */
public class SnowFlakeClient {

    /**
     * 起始时间戳
     */
    private static final long START_TIMESTAMP = 1704038400L; //2024-01-01 00:00:00

    /**
     * 各组成部分占用的位数
     * */
    /**
     * 时间戳
     */
    private static final long TIMESTAMP_BIT = 41;

    /**
     * 机器id
     */
    private static final long MACHINE_BIT = 10;

    /**
     * 序列号
     */
    private static final long SEQUENCE_BIT = 12;

    // 每一部分的最大值
    private static final long MAX_SEQUENCE = ~(-1L << SEQUENCE_BIT);
    private static final long MAX_MACHINE_NUM = ~(-1L << MACHINE_BIT);

    // 每一部分向左的位移
    private static final long MACHINE_LEFT = SEQUENCE_BIT;
    private static final long TIMESTAMP_LEFT = SEQUENCE_BIT + MACHINE_BIT;


    /**
     * 上一次生成id的时间戳（不断改变）
     */
    private static long lastTimeStamp = -1L;

    /**
     * 递增序列号
     */
    private static long sequence = 0L;

    /**
     * 生成雪花id
     */
    public static long nextId() {

        //1.获取当前时间戳
        long now = System.currentTimeMillis();

        //2.判断服务器是否时钟回拨
        if (now < lastTimeStamp) {
            throw new RuntimeException("服务器时钟回拨，可能会导致id不唯一");
        }

        //3.判断是否在同一毫秒
        if (now == lastTimeStamp) {
            //3.1同一毫秒内，就让序列号递增，注意不要超出最大范围
            sequence = (sequence + 1) & MAX_SEQUENCE;//做与运算就能去掉超出最高位的数字
            if (sequence == 0L) {
                //3.1.1序列号已经用完了，本毫秒内不再生成新id
                now = System.currentTimeMillis();
                while (now <= lastTimeStamp) {
                    now = System.currentTimeMillis();
                }
            }
        } else {
            //不在同一个毫秒，重置序列号
            sequence = 0L;
        }

        //更新时间戳
        lastTimeStamp = now;

        //4.组合成id：使用移位，以及或运算
        long id = ((now - START_TIMESTAMP) << TIMESTAMP_LEFT) | (IdConfig.machineId << MACHINE_LEFT) | sequence;

        return id;

    }

}

测试：

public class Test {
    public static void main(String[] args) {
        for (int i = 0; i < 100; i++) {
            System.out.println(Long.toBinaryString(SnowFlakeClient.nextId()));
        }
    }
}

结果：

110001110111110101001000111111101111111100000000000000000000000
110001110111110101001000111111110001001010000000000000000000000
110001110111110101001000111111110001001010000000000000000000001
110001110111110101001000111111110001001010000000000000000000010
110001110111110101001000111111110001001010000000000000000000011
110001110111110101001000111111110001001010000000000000000000100
110001110111110101001000111111110001001010000000000000000000101
110001110111110101001000111111110001001010000000000000000000110
110001110111110101001000111111110001001010000000000000000000111
110001110111110101001000111111110001001010000000000000000001000
110001110111110101001000111111110001001010000000000000000001001
110001110111110101001000111111110001001010000000000000000001010
110001110111110101001000111111110001001100000000000000000000000
110001110111110101001000111111110001001100000000000000000000001
110001110111110101001000111111110001001100000000000000000000010
110001110111110101001000111111110001001100000000000000000000011
110001110111110101001000111111110001001100000000000000000000100
110001110111110101001000111111110001001100000000000000000000101
110001110111110101001000111111110001001100000000000000000000110
110001110111110101001000111111110001001100000000000000000000111
110001110111110101001000111111110001001100000000000000000001000
110001110111110101001000111111110001001100000000000000000001001
110001110111110101001000111111110001001100000000000000000001010
110001110111110101001000111111110001001100000000000000000001011
110001110111110101001000111111110001001100000000000000000001100
110001110111110101001000111111110001001100000000000000000001101
110001110111110101001000111111110001001100000000000000000001110