2021年12月21日復盤雪花算法服務器時鍾偏移錯誤

本文轉載自查看原文 2021-12-21 19:40 2403 每日復盤

1、Mybatis plus默認對id為空的進行雪花算法或者UUID生成，但是我用的是select seq.nextval from dual的方式獲取的，這個本來也就是浪費資源去生成ID而已。但是沒想到。。。。服務器的時間居然比實際的時間多了20多秒，結果雪花算法在計算ID值的時候，判斷上一次的時間戳始終大於本次生成的一直報錯。

錯誤堆棧大概是這樣的：

Caused by: java.lang.RuntimeException: Clock moved backwards.  Refusing to generate id for 24227 milliseconds
        at com.baomidou.mybatisplus.core.toolkit.Sequence.nextId(Sequence.java:158) ~[mybatis-plus-core-3.4.1.jar:3.4.1]
        at com.baomidou.mybatisplus.core.incrementer.DefaultIdentifierGenerator.nextId(DefaultIdentifierGenerator.java:45) ~[mybatis-plus-core-3.4.1.jar:3.4.1]
        at com.baomidou.mybatisplus.core.incrementer.DefaultIdentifierGenerator.nextId(DefaultIdentifierGenerator.java:27) ~[mybatis-plus-core-3.4.1.jar:3.4.1]
        at com.baomidou.mybatisplus.core.MybatisParameterHandler.populateKeys(MybatisParameterHandler.java:133) ~[mybatis-plus-core-3.4.1.jar:3.4.1]
        at com.baomidou.mybatisplus.core.MybatisParameterHandler.process(MybatisParameterHandler.java:112) ~[mybatis-plus-core-3.4.1.jar:3.4.1]
        at java.util.ArrayList.forEach(ArrayList.java:1249) ~[?:1.8.0_121]
        at com.baomidou.mybatisplus.core.MybatisParameterHandler.processParameter(MybatisParameterHandler.java:79) ~[mybatis-plus-core-3.4.1.jar:3.4.1]
        at com.baomidou.mybatisplus.core.MybatisParameterHandler.<init>(MybatisParameterHandler.java:64) ~[mybatis-plus-core-3.4.1.jar:3.4.1]
        at com.baomidou.mybatisplus.core.MybatisXMLLanguageDriver.createParameterHandler(MybatisXMLLanguageDriver.java:35) ~[mybatis-plus-core-3.4.1.jar:3.4.1]
        at org.apache.ibatis.session.Configuration.newParameterHandler(Configuration.java:645) ~[mybatis-3.5.6.jar:3.5.6]
        at org.apache.ibatis.executor.statement.BaseStatementHandler.<init>(BaseStatementHandler.java:69) ~[mybatis-3.5.6.jar:3.5.6]
        at org.apache.ibatis.executor.statement.PreparedStatementHandler.<init>(PreparedStatementHandler.java:41) ~[mybatis-3.5.6.jar:3.5.6]
        at org.apache.ibatis.executor.statement.RoutingStatementHandler.<init>(RoutingStatementHandler.java:46) ~[mybatis-3.5.6.jar:3.5.6]
        at org.apache.ibatis.session.Configuration.newStatementHandler(Configuration.java:658) ~[mybatis-3.5.6.jar:3.5.6]
        at org.apache.ibatis.executor.SimpleExecutor.doUpdate(SimpleExecutor.java:48) ~[mybatis-3.5.6.jar:3.5.6]
        at org.apache.ibatis.executor.BaseExecutor.update(BaseExecutor.java:117) ~[mybatis-3.5.6.jar:3.5.6]
        at org.apache.ibatis.executor.CachingExecutor.update(CachingExecutor.java:76) ~[mybatis-3.5.6.jar:3.5.6]
        at sun.reflect.GeneratedMethodAccessor121.invoke(Unknown Source) ~[?:?]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_121]
        at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_121]
        at org.apache.ibatis.plugin.Invocation.proceed(Invocation.java:49) ~[mybatis-3.5.6.jar:3.5.6]
        at com.baomidou.mybatisplus.extension.plugins.MybatisPlusInterceptor.intercept(MybatisPlusInterceptor.java:83) ~[mybatis-plus-extension-3.4.1.jar:3.4.1]
        at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:61) ~[mybatis-3.5.6.jar:3.5.6]
        at com.sun.proxy.$Proxy176.update(Unknown Source) ~[?:?]
        at sun.reflect.GeneratedMethodAccessor121.invoke(Unknown Source) ~[?:?]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_121]
        at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_121]
        at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:63) ~[mybatis-3.5.6.jar:3.5.6]
        at com.sun.proxy.$Proxy176.update(Unknown Source) ~[?:?]
        at org.apache.ibatis.session.defaults.DefaultSqlSession.update(DefaultSqlSession.java:197) ~[mybatis-3.5.6.jar:3.5.6]
        at org.apache.ibatis.session.defaults.DefaultSqlSession.insert(DefaultSqlSession.java:184) ~[mybatis-3.5.6.jar:3.5.6]
        at sun.reflect.GeneratedMethodAccessor161.invoke(Unknown Source) ~[?:?]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_121]
        at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_121]
        at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:427) ~[mybatis-spring-2.0.6.jar:2.0.6]
        ... 85 more

分析下源碼com.baomidou.mybatisplus.core.toolkit.Sequence

    /**
     * 獲取下一個 ID
     *
     * @return 下一個 ID
     */
    public synchronized long nextId() {
        long timestamp = timeGen();
        //閏秒
        if (timestamp < lastTimestamp) {
            long offset = lastTimestamp - timestamp;
            if (offset <= 5) {
                try {
                    wait(offset << 1);
                    timestamp = timeGen();
                    if (timestamp < lastTimestamp) {
                        throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", offset));
                    }
                } catch (Exception e) {
                    throw new RuntimeException(e);
                }
            } else {
                throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", offset));
            }
        }

        if (lastTimestamp == timestamp) {
            // 相同毫秒內，序列號自增
            sequence = (sequence + 1) & sequenceMask;
            if (sequence == 0) {
                // 同一毫秒的序列數已經達到最大
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            // 不同毫秒內，序列號置為 1 - 3 隨機數
            sequence = ThreadLocalRandom.current().nextLong(1, 3);
        }

        lastTimestamp = timestamp;

        // 時間戳部分 | 數據中心部分 | 機器標識部分 | 序列號部分
        return ((timestamp - twepoch) << timestampLeftShift)
                | (datacenterId << datacenterIdShift)
                | (workerId << workerIdShift)
                | sequence;
    }