微服务架构id生成策略

小咪咪 2022-04-23 16:56 135阅读 0赞

## 1.id生成  ##

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3JpanU0NzEz_size_16_color_FFFFFF_t_70][]

## 2.分布式id生成器 ##

目前微服务架构盛行，在分布式系统中的操作中都会有一些全局性ID的需求,所以我们不能使用数据库本身的自增 功能来产生主键值，只能由程序来生成唯一的主键值。我们采用的是开源的twitter( 非官方中文惯称：推特.是国外 的一个网站，是一个社交网络及微博客服务) 的snowﬂake （雪花）算法。  
 ![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3JpanU0NzEz_size_16_color_FFFFFF_t_70 1][]

各个段解析：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3JpanU0NzEz_size_16_color_FFFFFF_t_70 2][]

默认情况下41bit的时间戳可以支持该算法使用到2082年，10bit的工作机器id可以支持1024台机器，序列号 支持1毫秒产生4096个自增序列id . SnowFlake的优点是，整体上按照时间自增排序，并且整个分布式系统内 不会产生ID碰撞(由数据中心ID和机器ID作区分)，并且效率较高，经测试，SnowFlake每秒能够产生26万ID 左右

//雪花算法代码实现
    public class IdWorker {
        // 时间起始标记点，作为基准，一般取系统的最近时间（一旦确定不能变动）
        private final static long twepoch = 1288834974657L;
        // 机器标识位数
        private final static long workerIdBits = 5L;
        // 数据中心标识位数
        private final static long datacenterIdBits = 5L;
        // 机器ID最大值
        private final static long maxWorkerId = -1L ^ (-1L << workerIdBits);
        // 数据中心ID最大值
        private final static long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
        // 毫秒内自增位
        private final static long sequenceBits = 12L;
        // 机器ID偏左移12位
        private final static long workerIdShift = sequenceBits;
        // 数据中心ID左移17位
        private final static long datacenterIdShift = sequenceBits + workerIdBits;
        // 时间毫秒左移22位
        private final static long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
    
        private final static long sequenceMask = -1L ^ (-1L << sequenceBits);
        /* 上次生产id时间戳 */
        private static long lastTimestamp = -1L;
        // 0，并发控制
        private long sequence = 0L;
    
        private final long workerId;
        // 数据标识id部分
        private final long datacenterId;
    
        public IdWorker(){
            this.datacenterId = getDatacenterId(maxDatacenterId);
            this.workerId = getMaxWorkerId(datacenterId, maxWorkerId);
        }
        /**
         * @param workerId
         *            工作机器ID
         * @param datacenterId
         *            序列号
         */
        public IdWorker(long workerId, long datacenterId) {
            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;
        }
        /**
         * 获取下一个ID
         *
         * @return
         */
        public synchronized long nextId() {
            long timestamp = timeGen();
            if (timestamp < lastTimestamp) {
                throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
            }
    
            if (lastTimestamp == timestamp) {
                // 当前毫秒内，则+1
                sequence = (sequence + 1) & sequenceMask;
                if (sequence == 0) {
                    // 当前毫秒内计数满了，则等待下一秒
                    timestamp = tilNextMillis(lastTimestamp);
                }
            } else {
                sequence = 0L;
            }
            lastTimestamp = timestamp;
            // ID偏移组合生成最终的ID，并返回ID
            long nextId = ((timestamp - twepoch) << timestampLeftShift)
                    | (datacenterId << datacenterIdShift)
                    | (workerId << workerIdShift) | sequence;
    
            return nextId;
        }
    
        private long tilNextMillis(final long lastTimestamp) {
            long timestamp = this.timeGen();
            while (timestamp <= lastTimestamp) {
                timestamp = this.timeGen();
            }
            return timestamp;
        }
    
        private long timeGen() {
            return System.currentTimeMillis();
        }
    
        /**
         * <p>
         * 获取 maxWorkerId
         * </p>
         */
        protected static long getMaxWorkerId(long datacenterId, long maxWorkerId) {
            StringBuffer mpid = new StringBuffer();
            mpid.append(datacenterId);
            String name = ManagementFactory.getRuntimeMXBean().getName();
            if (!name.isEmpty()) {
                /*
                 * GET jvmPid
                 */
                mpid.append(name.split("@")[0]);
            }
            /*
             * MAC + PID 的 hashcode 获取16个低位
             */
            return (mpid.toString().hashCode() & 0xffff) % (maxWorkerId + 1);
        }
    
        /**
         * <p>
         * 数据标识id部分
         * </p>
         */
        protected static long getDatacenterId(long maxDatacenterId) {
            long id = 0L;
            try {
                InetAddress ip = InetAddress.getLocalHost();
                NetworkInterface network = NetworkInterface.getByInetAddress(ip);
                if (network == null) {
                    id = 1L;
                } else {
                    byte[] mac = network.getHardwareAddress();
                    id = ((0x000000FF & (long) mac[mac.length - 1])
                            | (0x0000FF00 & (((long) mac[mac.length - 2]) << 8))) >> 6;
                    id = id % (maxDatacenterId + 1);
                }
            } catch (Exception e) {
                System.out.println(" getDatacenterId: " + e.getMessage());
            }
            return id;
        }
    }

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