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聊聊业务项目如何主动感知mysql是否存活

小心程序猿QAQ 2130

前言:

而今咱们对“checkmysqlis”可能比较重视,同学们都想要知道一些“checkmysqlis”的相关资讯。那么小编也在网上网罗了一些关于“checkmysqlis””的相关知识,希望我们能喜欢,同学们快快来学习一下吧!

前言

先前写过一篇文章聊聊如何利用redis实现多级缓存同步,里面讲到业务部门因数据库宕机,有技术提出当数据库宕机,切换到redis,今天我们就来聊聊如何触发这个切换动作?

1、方案一:利用异常机制

伪代码如下:

首先这个方案是不可行的,因为每次请求,还是先走到数据库逻辑,然后等抛出异常,这个时间会挺长的,业务上是无法接受的

2、方案二:主动进行mysql探活

实现思路: 可以利用数据库连接池检测有效连接的思路

实现方案

1、方式一:利用druid连接池的ValidConnectionChecker进行扩展

核心逻辑如下

@Slf4jpublic class MysqlConnectionCheck extends MySqlValidConnectionChecker {    private ApplicationContext applicationContext;    public MysqlConnectionCheck(ApplicationContext applicationContext) {        this.applicationContext = applicationContext;    }    @Override    public boolean isValidConnection(Connection conn, String validateQuery, int validationQueryTimeout) throws Exception {      return checkMySQLCommunications(conn,validateQuery,validationQueryTimeout);    }    private boolean checkMySQLCommunications (Connection conn, String validateQuery, int validationQueryTimeout) {        boolean validConnection = false;        try {            validConnection = super.isValidConnection(conn, validateQuery, validationQueryTimeout);        } catch (Exception e) {        }        if(validConnection){            boolean b = MySQLCommunicationsHolder.isMySQLCommunicationsException.compareAndSet(true, false);            if(b){                CommunicationsHealthEvent event = CommunicationsHealthEvent.builder().conn(conn).build();                applicationContext.publishEvent(event);            }        }        return validConnection;    }}复制代码

在yml配置我们自定义的检测器

spring:    datasource:        type: com.alibaba.druid.pool.DruidDataSource        driverClassName: ${DRIVER_CALSS_NAME:com.mysql.cj.jdbc.Driver}        url: ${DATASOURCE_URL:jdbc:mysql://localhost:3306/demo?useUnicode=true&characterEncoding=utf8&useSSL=false&serverTimezone=Asia/Shanghai}        username: ${DATASOURCE_USERNAME:root}        password: ${DATASOURCE_PWD:123456}        druid:            # 指定连接的有效检查类            valid-connection-checker-class-name: com.github.lybgeek.db.check.test.user.check.MysqlConnectionCheck 复制代码

这个方案也是不大行的,后面翻了一下druid源码。当数据库抛出不可恢复的异常时,比如网络抖动,异常断开,druid会触发exceptionSorter,抛弃连接。而CreateConnectionThread会检测是否需要创建连接,如果不需要,他就会进行等待。当连接不够时,会调用

com.alibaba.druid.pool.DruidAbstractDataSource#createPhysicalConnection()复制代码

进行创建,同时isValidConnection也是在这个方法里面进行连接验证,但这边就有问题,就是当数据库宕机了,就创建不了连接,因此就进入异常流程,isValidConnection是没法执行的

2、方式二:参考druid的检测连接逻辑,额外编写定时器触发检测逻辑

核心代码块:

public class ValidConnectionCheckerAdapter implements ValidConnectionChecker {    private DbCheckProperies dbCheckProperies;    public ValidConnectionCheckerAdapter(DbCheckProperies dbCheckProperies) {        this.dbCheckProperies = dbCheckProperies;    }    @Override    public boolean isValidConnection(Connection conn, String query, int validationQueryTimeout) throws SQLException {        boolean valid = checkConnection(conn, query, validationQueryTimeout);        // unexcepted branch        if (valid && isMysql()) {            long lastPacketReceivedTimeMs = MySqlUtils.getLastPacketReceivedTimeMs(conn);            if (lastPacketReceivedTimeMs > 0) {                long mysqlIdleMillis = System.currentTimeMillis() - lastPacketReceivedTimeMs;                if (lastPacketReceivedTimeMs > 0                        && mysqlIdleMillis >= dbCheckProperies.getTimeBetweenEvictionRunsMillis()) {                    return false;                }            }        }        return valid;    }    private boolean checkConnection(Connection conn, String query, int validationQueryTimeout) throws SQLException {        if (query == null || query.length() == 0) {            return true;        }        if(conn == null){            return false;        }        Statement stmt = null;        ResultSet rs = null;        try {            stmt = conn.createStatement();            if (validationQueryTimeout > 0) {                stmt.setQueryTimeout(validationQueryTimeout);            }            rs = stmt.executeQuery(query);            return true;        } finally {            JdbcUtils.close(rs);            JdbcUtils.close(stmt);        }    }复制代码
 @Override    public void afterPropertiesSet() throws Exception {        executorService.scheduleWithFixedDelay(new DbCheckTask(),0,dbCheckProperies.getTimeBetweenEvictionRunsMillis(), TimeUnit.MILLISECONDS);    }        private class DbCheckTask implements Runnable{        @Override        public void run() {            SQLException sqlException = null;            Connection conn = dbConnManger.getConn();            try {                boolean validConnection = validConnectionChecker.isValidConnection(conn, dbCheckProperies.getValidationQuery(), dbCheckProperies.getValidationQueryTimeout());                if(validConnection){                    boolean b = MySQLCommunicationsHolder.isMySQLCommunicationsException.compareAndSet(true, false);                    if(b){                        CommunicationsHealthEvent event = CommunicationsHealthEvent.builder().conn(conn).build();                        applicationContext.publishEvent(event);                    }                }else{                   sqlException = new SQLException("connection is invalid","10040");                }            } catch (SQLException e) {                 log.error("{}",e);                 sqlException = e;                 dbConnManger.closeConnection();                 conn = null;            }            if(sqlException != null){                MySQLCommunicationsHolder.isMySQLCommunicationsException.compareAndSet(false, true);                CommunicationsUnHealthEvent event = CommunicationsUnHealthEvent.builder().sqlException(sqlException).build();                applicationContext.publishEvent(event);            }        }    } 复制代码
总结

其实mysql的探活实现方式有很多种,本文的实现检测逻辑是直接套用druid的检测连接逻辑,之前对druid的使用,基本上就是停留在配置上,没过多关注。

为了写这篇文章,特地翻了一下druid的源码,主要是因为之前以为扩展ValidConnectionChecker就行了,后面发现行不通。就看了一下源码,发现druid的设计思路挺好的,有些实现思想是我们在日常开发中,可以借鉴使用的。还有druid里面有些跟数据库相关的util,也是可以直接拿过来用的。

原文链接:

标签: #checkmysqlis