可实现的全局唯一有序ID生成策略
- 2019 年 10 月 25 日
- 笔记
在博客园搜素全局唯一有序ID，罗列出来的文章大致讲述了以下几个问题，常见的生成全局唯一id的常见方法 ：使用数据库自动增长序列实现 ； 使用UUID实现； 使用redis实现； 使用Twitter的snowflake算法实现；使用数据库+本地缓存实现。作为一个记录性质的博客，简单总结一下。
在实际的生产场景中，经常会出现如下的情况比方说订单号：D channelNo 流水号 样例PSDK1600000001, PSDK1600000002, PSDK1600000003… 这种具有业务意义的全局唯一id且有序自增。先来看一下使用比较多的Twitter的snowflake算法，snowflake生成的ID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datacenter和workerId作区分），并且效率较高。经测试snowflake每秒能够产生26万个ID。一个简单的实现如下：
/** * Twitter的分布式自增ID雪花算法snowflake **/ public class SnowFlake { /** * 起始的时间戳 */ private final static long START_STMP = 1480166465631L; /** * 每一部分占用的位数 */ private final static long SEQUENCE_BIT = 12; //序列号占用的位数 private final static long MACHINE_BIT = 5; //机器标识占用的位数 private final static long DATACENTER_BIT = 5;//数据中心占用的位数 /** * 每一部分的最大值 */ private final static long MAX_DATACENTER_NUM = -1L ^ (-1L << DATACENTER_BIT); private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT); private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT); /** * 每一部分向左的位移 */ private final static long MACHINE_LEFT = SEQUENCE_BIT; private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT; private final static 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 public 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 */ public synchronized long nextId() { long currStmp = getNewstmp(); 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 = getNewstmp(); while (mill <= lastStmp) { mill = getNewstmp(); } return mill; } private long getNewstmp() { return System.currentTimeMillis(); } public static void main(String[] args) { SnowFlake snowFlake = new SnowFlake(1, 1); long start = System.currentTimeMillis(); for (int i = 0; i < 10; i++) { System.out.println(snowFlake.nextId()); } System.out.println(System.currentTimeMillis() - start); } }
算法中引入了时间因子，所以可以保证生成的id唯一且有序，但是满足不了业务字段+流水号有序自增的要求。如果在此基础上再配合使用数据库本地缓存自然也是可以实现的，不过复杂化了。上述代码执行两次结果如下：
385063405393940480 385063405393940481 385063405393940482 385063405393940483 385063405393940484 385063405393940485 385063405393940486 385063405393940487 385063405398134784 385063405398134785 385064572152844288 385064572152844289 385064572152844290 385064572152844291 385064572152844292 385064572152844293 385064572152844294 385064572152844295 385064572152844296 385064572152844297
简单的方法就是我们放弃自己造轮子的思想。mongodb中数据的基本单元称为document，在一个特定集合内部需要唯一的标识文档，因此mongdb中存储的文档都由一个‘_id’键，这个键的值可以是任意类型的ObjectId，要求不同的机器都能用全局唯一的同种方法方便的生成它。因此不能使用自增主键，ObjectId 底层也是借鉴了雪花算法，使用12字节的存储空间 |0|1|2|3|4|5|6 |7|8|9|10|11| |时间戳 |机器ID|PID|计数器| 前四个字节时间戳是从标准纪元开始的时间戳，单位为秒 。时间戳保证秒级唯一，机器ID保证设计时考虑分布式，避免时钟同步，PID保证同一台服务器运行多个mongod实例时的唯一性，最后的计数器保证同一秒内的唯一性。
mongo在spring boot中的引入和配置，此处不再介绍。
创建model类
package com.slowcity.admin.generate.dbmodel; import java.io.Serializable; public class BaseSequence implements Serializable{ private static final long serialVersionUID = 475722757687764546L; private String id; private String name; private Long sequence; public String getId() { return id; } public void setId(String id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Long getSequence() { return sequence; } public void setSequence(Long sequence) { this.sequence = sequence; } @Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + ((id == null) ? 0 : id.hashCode()); result = prime * result + ((name == null) ? 0 : name.hashCode()); result = prime * result + ((sequence == null) ? 0 : sequence.hashCode()); return result; } @Override public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass() != obj.getClass()) return false; BaseSequence other = (BaseSequence) obj; if (id == null) { if (other.id != null) return false; } else if (!id.equals(other.id)) return false; if (name == null) { if (other.name != null) return false; } else if (!name.equals(other.name)) return false; if (sequence == null) { if (other.sequence != null) return false; } else if (!sequence.equals(other.sequence)) return false; return true; } @Override public String toString() { return "BaseSequence [id=" + id + ", name=" + name + ", sequence=" + sequence + "]"; } }
public class DigitalTaskSequence extends BaseSequence{ private static final long serialVersionUID = -7287622688931253780L; }
import org.springframework.data.annotation.Id; import org.springframework.data.mongodb.core.mapping.Document; import org.springframework.stereotype.Component; @Component @Document(collection = "dm_id_task") public class DigitalTaskSequenceMG extends DigitalTaskSequence { private static final long serialVersionUID = -425011291271386371L; @Id @Override public String getId() { return super.getId(); } }
service
import java.util.List; import com.slowcity.admin.generate.dbmodel.BaseSequence; public interface SequenceGenericService { public String generateId(Class<? extends BaseSequence> clazz); List<BaseSequence> initAllId(); }
import java.util.ArrayList; import java.util.List; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.springframework.stereotype.Service; import org.springframework.transaction.annotation.Transactional; import com.slowcity.admin.generate.dbmodel.BaseSequence; import com.slowcity.admin.generate.dbmodel.DigitalTaskSequenceMG; import com.slowcity.admin.generate.repository.SequenceGenericRepository; import com.slowcity.admin.generate.service.SequenceGenericService; @Service @Transactional public class SequenceGenericServiceImpl implements SequenceGenericService { private static final Logger log = LoggerFactory.getLogger(SequenceGenericServiceImpl.class); private SequenceGenericRepository sequenceGenericRepository; public SequenceGenericServiceImpl(SequenceGenericRepository sequenceGenericRepository) { this.sequenceGenericRepository = sequenceGenericRepository; } @Override public String generateId(Class<? extends BaseSequence> clazz) { String id = sequenceGenericRepository.generateId(clazz); log.info("{} generate {}", clazz.getName(), id); return id; } @Override public List<BaseSequence> initAllId() { List<BaseSequence> baseSequenceList = new ArrayList<>(), baseSequenceResultList = new ArrayList<>(); DigitalTaskSequenceMG digitalTaskSequenceMG = new DigitalTaskSequenceMG(); digitalTaskSequenceMG.setName("sequence"); digitalTaskSequenceMG.setSequence(1210000000000000000L); //1210可以代表业务号 000000000000000代表自增流水号
baseSequenceList.add(digitalTaskSequenceMG); for (BaseSequence baseSequence:baseSequenceList) { BaseSequence resultSequence = sequenceGenericRepository.initAllId(baseSequence); if(resultSequence != null){ baseSequenceResultList.add(resultSequence); } } return baseSequenceResultList; } }
数据实现层
import com.slowcity.admin.generate.dbmodel.BaseSequence; public interface SequenceGenericRepository { public String generateId(Class<? extends BaseSequence> clazz); BaseSequence initAllId(BaseSequence Sequence); }
import java.util.List; import java.util.Map; import java.util.stream.Collectors; import org.springframework.data.mongodb.core.MongoTemplate; import org.springframework.data.mongodb.core.query.Criteria; import org.springframework.data.mongodb.core.query.Query; import org.springframework.data.mongodb.core.query.Update; import org.springframework.stereotype.Component; import com.slowcity.admin.generate.dbmodel.BaseSequence; import com.slowcity.admin.generate.repository.SequenceGenericRepository; @Component public class SequenceMongoGenericRepository implements SequenceGenericRepository { private Map<Class,Class<? extends BaseSequence>> baseSequenceMap; private MongoTemplate mongoTemplate; public SequenceMongoGenericRepository(List<BaseSequence> baseSequences, MongoTemplate mongoTemplate){ baseSequenceMap = baseSequences.stream() .collect(Collectors.toMap(baseSequence -> baseSequence.getClass().getSuperclass(), BaseSequence::getClass)); this.mongoTemplate = mongoTemplate; } @Override public String generateId(Class<? extends BaseSequence> clazz) { Class<? extends BaseSequence> childClazz = baseSequenceMap.get(clazz); if(childClazz != null) { Query query = new Query(Criteria.where("name").is("sequence")); Update update = new Update().inc("sequence", 1); Object dbm = mongoTemplate.findAndModify(query, update, childClazz); if(dbm != null) { BaseSequence bs = (BaseSequence)dbm; return String.valueOf(bs.getSequence()); } } return null; } @Override public BaseSequence initAllId(BaseSequence Sequence) { Query query = new Query(Criteria.where("name").is("sequence")); Class clazz = Sequence.getClass(); List<? extends BaseSequence> list = mongoTemplate.find(query,clazz); if(list.isEmpty()){ mongoTemplate.save(Sequence); return Sequence; } return null; } }
controller
import java.util.List; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RequestMethod; import org.springframework.web.bind.annotation.RestController; import com.slowcity.admin.generate.dbmodel.BaseSequence; import com.slowcity.admin.generate.dbmodel.DigitalTaskSequence; import com.slowcity.admin.generate.service.SequenceGenericService; /** * id生成器 * @author moona * */ @RestController @RequestMapping("/generateId/task") public class TaskGenerateIdController { @Autowired private SequenceGenericService sequenceGenericService; @RequestMapping(value = "/taskId", method = RequestMethod.GET) public String generateTaskId() { return sequenceGenericService.generateId(DigitalTaskSequence.class); } @RequestMapping(value = "/init", method = RequestMethod.GET) public List<BaseSequence> generateTaskIdinit() { return sequenceGenericService.initAllId(); } }
执行初始化调用方法
对应数据库
开始测试生成id
第一次调用：
第2次调用
第10次调用
此时再查看数据库，序列已经到1210000000000000011 下次调用直接取值了。真正做到了了分布式满足业务的自增全局唯一索引。mongo底层是原子性的，所以也不会出现并发的问题。如果将id生成策略部署成单台机器服务，则可以满足不同服务不同业务的需求，真正做到可定制可扩展。尽可放心使用。
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