基于本地缓存制作一个分库分表的分布式ID生成器

引言：

代码在 https://gitee.com/lbmb/mb-live-app 中【mb-live-id-generate-provider】模块里面如果喜欢希望大家给给star 项目还在持续更新中。

背景介绍

项目整体架构是基于springboot 3.0 开发 rpc 调用采用 dubbo
注册配置中心使用 nacos 采用sharding-jdbc 来实现分库分表。
基于以上情况我想生成分布式id。再根据生成的分布式id 存到不同的表中
例如 id 1000 存在 user01表 id 1001 存到 user02表，然后sharding-jdbc会根据我们

基础成长

可以学习到多线程、线程池的使用和设计
分布式id器的优化策略（预加载、类似hashmap扩容）

首先我们需要设计一张id策略表

CREATE TABLE `t_id_generate_config` (
  `id` int NOT NULL AUTO_INCREMENT COMMENT '主键 id',
  `remark` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL COMMENT '描述',
  `next_threshold` bigint DEFAULT NULL COMMENT '当前 id 所在阶段的阈\n值',
  `init_num` bigint DEFAULT NULL COMMENT '初始化值',
  `current_start` bigint DEFAULT NULL COMMENT '当前 id 所在阶段的开始\n值',
  `step` int DEFAULT NULL COMMENT 'id 递增区间',
  `is_seq` tinyint DEFAULT NULL COMMENT '是否有序（0 无序，1 有序）',
  `id_prefix` varchar(60) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL COMMENT '业务前缀码，如果没有则返回\n时不携带',
  `version` int NOT NULL DEFAULT '0' COMMENT '乐观锁版本号',
  `create_time` datetime DEFAULT CURRENT_TIMESTAMP COMMENT '创建时\n间',
  `update_time` datetime DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '更新时间',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

INSERT INTO `t_id_generate_config` (`id`, `remark`,
`next_threshold`, `init_num`, `current_start`, `step`, `is_seq`,`id_prefix`, `version`, `create_time`, `update_time`)
VALUES
(1, '用户 id 生成策略', 10050, 10000, 10000, 50, 0,
'user_id', 0, '2023-05-23 12:38:21', '2023-05-23 23:31:45');

定义全局变量
变量解析

localSeqIdBOMap 缓存中可分配的分布式id（有序id）
localUnSeqIdBOMap 缓存中可分配的分布式id（无序id）
SEQ_ID = 1; 判断是否为有序id 的操作（扩容存取等）
threadPoolExecutor 移步线程池（用来异步动态扩容缓存的可分配id 池）
semaphoreMap 信号量存放map 防止多线程环境下多次重复触发异步扩容线程池。参考 ConcurrentHashMap 的扩容实现（ConcurrentHashMap ：）。
UNDATE_RATE：动态扩容阀值


    private static final Logger LOGGER = LoggerFactory.getLogger(IdGenerateService.class);
    private static Map<Integer, LocalSeqIdBO> localSeqIdBOMap = new ConcurrentHashMap<Integer, LocalSeqIdBO>();
    private static Map<Integer, LocalUnSeqIdBO> localUnSeqIdBOMap = new ConcurrentHashMap<Integer, LocalUnSeqIdBO>();
    private static final Integer SEQ_ID = 1;
    private static ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(8, 16, 3, TimeUnit.SECONDS, new ArrayBlockingQueue<>(1000),
            new ThreadFactory() {
                @Override
                public Thread newThread(Runnable r) {
                    Thread thread = new Thread(r);
                    thread.setName("id-generate-thread-" + ThreadLocalRandom.current().nextInt(1000));
                    return null;
                }
            });

    /**
     * 使用Semaphore 信号量来防止多线程并发 多次刷新id段
     */
    private static Map<Integer, Semaphore> semaphoreMap = new ConcurrentHashMap<>();

    /**
     * id段刷新优化 阈值为0.75 达到百分之75 执行异步任务创建 优化
     */
    private static final float UNDATE_RATE = 0.75f;

有序 id 生成器

 /**
     * 有序id生成器
     *
     * @param id
     * @return
     */
    @Override
    public Long geSeqId(Integer id) {
        if (id == null) {
            LOGGER.error("[geSeqId] id is error,id is{}", id);
            return null;
        }
        LocalSeqIdBO localSeqIdBO = localSeqIdBOMap.get(id);
        if (localSeqIdBO == null) {
            LOGGER.error("[geSeqId] localSeqIdBO is null,id is{}", id);
            return null;
        }

        /**
         * 异步 预执行刷新id段
         */
        this.refreshLocalSeqId(localSeqIdBO);
        long andIncrement = localSeqIdBO.getCurrentNum().getAndIncrement();

        if (andIncrement> localSeqIdBO.getNextThreshold()) {
            LOGGER.error("[geSeqId] id  is over limit,id is{}", id);
            return null;
        }

        // 获取当前id 直增
        return andIncrement;
    }

代码解读从数据库读取到对应的方案（有序id 和无序id 方案会有当前可用的 id段开始值和结束值以及步长等信息）
LocalSeqIdBO localSeqIdBO = localSeqIdBOMap.get(id);
预扩容：例如当前可用id段是 1000-1500 判断 1000-1500 的id 被使用超过了百分之75 就动态将id池进行扩容

this.refreshLocalSeqId(localSeqIdBO);

取出当前已使用的id 最大值并且进行+1
long andIncrement = localSeqIdBO.getCurrentNum().getAndIncrement();

// 优化逻辑如果当前已经用的id +1 后超过了当前id池的最大值则不会生成id。例：当前id池最大是 1500 但是取出的当前已用的id 为 1500 则加一后是1501 超过了id池最大值1500 则不会生成id 继而下一次操作会扩容id池
if (andIncrement> localSeqIdBO.getNextThreshold()) {
LOGGER.error(“[geSeqId] id is over limit,id is{}”, id);
return null;
}

异步刷新本地 id池

 /**
     * 刷新本地有序的id段
     *
     * @param localSeqIdBO
     */
    private void refreshLocalSeqId(LocalSeqIdBO localSeqIdBO) {
        // 当前 id字段区间值
        long step = localSeqIdBO.getNextThreshold() - localSeqIdBO.getCurrentStart();
        /**
         * 使用Semaphore 信号量来防止多线程并发 多次刷新id段
         * 防止没扩容完成的时候过多线程进入到 if里面
         */
        if (localSeqIdBO.getCurrentNum().get() - localSeqIdBO.getCurrentStart() > step * UNDATE_RATE) {

            Semaphore semaphore = semaphoreMap.get(localSeqIdBO.getId());
            if (semaphore == null) {
                LOGGER.error("semaphore is null ,id is{}", localSeqIdBO.getId());
                return;

            }
            boolean acquireStatus = semaphore.tryAcquire();
            if (acquireStatus) {
                // 异步进行同步id字段的操作
                LOGGER.info("尝试开始进行同步id段的同步操作");
                threadPoolExecutor.execute(new Runnable() {
                    @Override
                    public void run() {
                        try {
                            IdGeneratePO idGeneratePO = mapper.selectById(localSeqIdBO.getId());
                            tryUpdateMysqlRecord(idGeneratePO);
                            // 释放semaphore资源


                        } catch (Exception e) {
                            LOGGER.error("[refreshLocalSeqId] error is {}", e);
                        } finally {
                            semaphoreMap.get(localSeqIdBO.getId()).release();
                            LOGGER.info("有序id段同步完成，id is {}", localSeqIdBO.getId());
                        }

                    }
                });
            }


        }

    }

初次落第一批id数据到id池

spring 容器启动的时候在初始化Bean后会回调这个方法

   //spring 启动的时候 bean 初始化的时候会回调这里
    @Override
    public void afterPropertiesSet() throws Exception {

        List<IdGeneratePO> idGeneratePOList = mapper.selectAll();
        for (IdGeneratePO idGeneratePO : idGeneratePOList) {
            tryUpdateMysqlRecord(idGeneratePO);
            semaphoreMap.put(idGeneratePO.getId(), new Semaphore(1));
        }

    }

更新数据库里面的 id字段占用位置信息并且尝试将已更新的id 段写入到缓存

   /**
     * 更新mysql里面的分布式id的配置信息，占用对应id段
     *
     * @param idGeneratePO
     */
    private void tryUpdateMysqlRecord(IdGeneratePO idGeneratePO) {

        int updateResult = mapper.updateNewIdCountAndVersion(idGeneratePO.getId(), idGeneratePO.getVersion());
        if (updateResult > 0) {
            localIdBoHandler(idGeneratePO);
            return;
        }
        for (int i = 0; i < 3; i++) {
            IdGeneratePO newIdGeneratePO = mapper.selectById(idGeneratePO.getId());

            updateResult = mapper.updateNewIdCountAndVersion(idGeneratePO.getId(), idGeneratePO.getVersion());
            if (updateResult > 0) {
                localIdBoHandler(idGeneratePO);
//                LocalSeqIdBO localSeqIdBO = new LocalSeqIdBO();
//                AtomicLong atomicLong = new AtomicLong(idGeneratePO.getCurrentStart());
//                localSeqIdBO.setId(idGeneratePO.getId() );
//                localSeqIdBO.setCurrentNum(atomicLong );
//                localSeqIdBO.setCurrentStart(idGeneratePO.getCurrentStart() );
//                localSeqIdBO.setNextThreshold(idGeneratePO.getNextThreshold()  );
//                localSeqIdBO.setCurrentNum(atomicLong );
//                localSeqIdBOMap.put(localSeqIdBO.getId(),localSeqIdBO);
                return;
            }

        }
        throw new RuntimeException("表id字段占用失败, 竞争过于激烈 id is :" + idGeneratePO.getId());
    }

将更新的id段实际落到缓存

/**
     * 专门处理如何将id对象放入本地缓存中
     *
     * @param idGeneratePO
     */
    private void localIdBoHandler(IdGeneratePO idGeneratePO) {
        long currentStart = idGeneratePO.getCurrentStart();
        long nextThreshold = idGeneratePO.getNextThreshold();
        long currentNum = currentStart;
        // 判断数据库取出来的id配置是有序还是无序 1 有序 非 1 无序
        if (idGeneratePO.getIsSeq() == SEQ_ID) {
            // 有序存储
            LocalSeqIdBO localSeqIdBO = new LocalSeqIdBO();
            AtomicLong atomicLong = new AtomicLong(currentStart);
            localSeqIdBO.setId(idGeneratePO.getId());
            localSeqIdBO.setCurrentStart(currentStart);
            localSeqIdBO.setNextThreshold(nextThreshold);
            localSeqIdBO.setCurrentNum(atomicLong);
            localSeqIdBOMap.put(localSeqIdBO.getId(), localSeqIdBO);
        } else {
            LocalUnSeqIdBO localUnSeqIdBO = new LocalUnSeqIdBO();
            localUnSeqIdBO.setId(idGeneratePO.getId());

            localUnSeqIdBO.setCurrentStart(currentStart);
            localUnSeqIdBO.setNextThreshold(nextThreshold);
            long begin = idGeneratePO.getCurrentStart();
            long end = idGeneratePO.getNextThreshold();
            ConcurrentLinkedQueue idQueue = new ConcurrentLinkedQueue();
            ArrayList<Long> idList = new ArrayList<>();
            for (long i = begin; i < end; i++) {
                idList.add(i);
            }
            // 无序操作将有序集合打乱
            Collections.shuffle(idList);
            idQueue.addAll(idList);
            localUnSeqIdBO.setIdQueue(idQueue);
            localUnSeqIdBOMap.put(localUnSeqIdBO.getId(), localUnSeqIdBO);

        }
    }

mapper 内容

@Mapper
public interface IdGenerateMapper extends BaseMapper<IdGeneratePO> {

    //    @Update("update t_id_generate_config set next_threshold = next_threshold + step,current_start=current_start + step , version = version + 1 where id = #{id} and version = #{version}")
//    int updateNewIdCountAndVersion(@Param("id") int id, @Param("version") int version);
    @Update("update t_id_generate_config set next_threshold=next_threshold+step," +
            "current_start=current_start+step,version=version+1 where id =#{id} and version=#{version}")
    int updateNewIdCountAndVersion(@Param("id") int id, @Param("version") int version);

    @Select("select * from t_id_generate_config")
    List<IdGeneratePO> selectAll();
}