分布式自增序列的实现(一) ---分布式序号生成器

刺骨的言语ヽ痛彻心扉 2022-04-14 04:47 233阅读 0赞

# 问题来源： #

微服务的框架，有的服务部署了多个实例，同时需要全局的自增id，当然使用uuid作为id是可以不用关系id的生成，但是如果要是序列sequence就需要自己实现id的生成，但是分布式环境下如何保证不会重复生成相同的id？

# 解决办法 #

1， 使用分布式锁，每次生成sequence时先获取全局锁，然后获取sequence，接着sequence+1并保存到持久存储中，最后释放锁。  
2，使用已有的框架提供分布式锁的，例如Redis，ZooKeeper。

本文选择使用zookeeper作为例子， 具体代码在[这里][Link 1]，欢迎加星，fork

# 具体实现 #

我使用zk的官方client，zk还有非常好用的curator客户端。

因此pom文件需要添加如下依赖

<dependency>
                <groupId>org.apache.zookeeper</groupId>
                <artifactId>zookeeper</artifactId>
                <version>3.4.9</version>
            </dependency>

具体示例代码如下，本代码非生产级别代码，只是作为示例。

package com.yq;
    
    
    import org.apache.zookeeper.CreateMode;
    import org.apache.zookeeper.ZooDefs;
    import org.apache.zookeeper.ZooKeeper;
    import org.apache.zookeeper.data.Stat;
    import org.slf4j.Logger;
    import org.slf4j.LoggerFactory;
    
    import java.util.List;
    
    /** * Simple to Introduction * className: ZKDemoOneApplication * * @author EricYang * @version 2018/8/24 23:43 */
    
    public class ZKClientSequenceApp { 
        private static ZooKeeper zk = null;
        private static final Logger log = LoggerFactory.getLogger(ZKClientSequenceApp.class);
        private static final String ZK_SERVERS = "127.0.0.1:2181";
        private static final int SESSION_TIME = 2000;
        private static final String PARENT_PATH_NAME_TEST = "/yqseq_test001";
        private static final String CHILD_PATH_NAME_TEST = "/yqseq_test001/";
        public static void main(String[] args) throws Exception { 
            zk = new ZooKeeper(ZK_SERVERS,SESSION_TIME, null);
            Stat stat = zk.exists(PARENT_PATH_NAME_TEST, null);
            if (stat == null) { 
                String zkParentPath = zk.create(PARENT_PATH_NAME_TEST, "helloWorld".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
                log.info("zkParentPath={}", zkParentPath);
            }
    
            String zkPath = zk.create(CHILD_PATH_NAME_TEST, "helloWorld".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT_SEQUENTIAL);
            log.info("zkPath={}", zkPath);
            List<String> children = zk.getChildren(PARENT_PATH_NAME_TEST, null);
    
            for(String seq : children) { 
                log.info("seq={}", seq);
            }
    
            log.info("start done.");
        }
    }

关于zookeeper如何保证CreateMode.PERSISTENT\_SEQUENTIAL的 path不会重复后面，请参考  
1， API文档http://zookeeper.apache.org/doc/current/api/index.html，

PERSISTENT_SEQUENTIAL
    
        public static final CreateMode PERSISTENT_SEQUENTIAL
    
        The znode will not be automatically deleted upon client's disconnect, and its name will be appended with a monotonically increasing number.

2，zookeeper关于Sequence Nodes 介绍  
[http://zookeeper.apache.org/doc/current/zookeeperProgrammers.html\#Sequence+Nodes+--+Unique+Naming][http_zookeeper.apache.org_doc_current_zookeeperProgrammers.html_Sequence_Nodes_--_Unique_Naming]  
When creating a znode you can also request that ZooKeeper append a monotonically increasing counter to the end of path. This counter is unique to the parent znode. The counter has a format of %010d – that is 10 digits with 0 (zero) padding (the counter is formatted in this way to simplify sorting), i.e. “  0000000001”. See Queue Recipe for an example use of this feature. Note: the counter used to store the next sequence number is a signed int (4bytes) maintained by the parent node, the counter will overflow when incremented beyond 2147483647 (resulting in a name “  \-2147483648”).

程序简单介绍：。  
程序每运行一次就或生成一个新的自增1的path， path就是sequece, 例如0000000001。sequence是10位，也就是最大可以达到10亿，一般我们系统针对单个对象10亿够用了，如果不够的可以设置两个序列，分别为主序列和副序列，这样就足够多了。  
本文没有删除旧的sequence，实际项目中最好需要获取id后，删除旧的序列，要不然zk的path会越来越多.

# 截图 #

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3J1c3NsZQ_size_16_color_FFFFFF_t_70]

[Link 1]: https://github.com/yqbjtu/SpringCloudTutorials/blob/master/ZKClientDemo/src/main/java/com/yq/ZKClientSequenceApp.java
[http_zookeeper.apache.org_doc_current_zookeeperProgrammers.html_Sequence_Nodes_--_Unique_Naming]: http://zookeeper.apache.org/doc/current/zookeeperProgrammers.html#Sequence+Nodes+--+Unique+Naming
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3J1c3NsZQ_size_16_color_FFFFFF_t_70]: /images/20220414/b2985765b9da4c3bbd967c0dc0487d78.png