阿里巴巴数据源Druid使用时报discard connection异常，为啥

Posted 2023-03-20

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参考技术A 2014-11-06 22:36:28,537 ERROR [com.alibaba.druid.pool.DruidDataSource] - discard connection
com.mysql.jdbc.CommunicationsException: The last communications with the server was 28816 seconds ago, which is longer than the server configured value of 'wait_timeout'. You should consider either expiring and/or testing connection validity before use in your application, increasing the server configured values for client timeouts, or using the Connector/J connection property 'autoReconnect=true' to avoid this problem.

配置了testWhileIdle=true，validationQuery=SELECT 'x'

timeBetweenEvictionRunsMillis=60000

minEvictableIdleTimeMillis=300000本回答被提问者和网友采纳

解决druid新版本报错 discard long time none received connection.

问题现象

本人使用的druid版本为1.2.1，再开发时，console控制台总是时不时打印一段：

 discard long time none received connection. jdbcUrl : xxxx

看着就很蛋疼，于是本着非主流不负责的态度就上网寻求问题原因😛

产生原因

网上搜罗了一圈，也算知晓了问题所在，查看源码：
在com.alibaba.druid.pool.DruidAbstractDataSource，

if (valid && isMySql)  // unexcepted branch
    long lastPacketReceivedTimeMs = MySqlUtils.getLastPacketReceivedTimeMs(conn);
    if (lastPacketReceivedTimeMs > 0) 
        long mysqlIdleMillis = currentTimeMillis - lastPacketReceivedTimeMs;
        if (lastPacketReceivedTimeMs > 0 //
                && mysqlIdleMillis >= timeBetweenEvictionRunsMillis) 
            discardConnection(holder);
            String errorMsg = "discard long time none received connection. "
                    + ", jdbcUrl : " + jdbcUrl
                    + ", version : " + VERSION.getVersionNumber()
                    + ", lastPacketReceivedIdleMillis : " + mysqlIdleMillis;
            LOG.warn(errorMsg);
            return false;

这段代码大致意思就是如果一个连接空闲超过60s，就丢弃之（holder）并且打印一条warn日志。

druid为什么会丢弃连接池中空闲仅60s的连接呢？网上有些人的说法是阿里为了提升数据库服务器的处理能力。

解决办法

给druid加一条配置： druid.mysql.usePingMethod=false
原理是让验证空闲连接不使用mysql的ping方法，而是使用select 1，这样每次进入上面提到的源码中时，时间都会刷新，就不会超过60s啦。
具体做法有两种：

运行时配置
即在运行参数中增加：在运行参数中增加：-Ddruid.mysql.usePingMethod=false

类文件配置
在项目的DruidConfig类中新增加：

/*
* 解决druid 日志报错：discard long time none received connection:xxx
* */
@PostConstruct
public void setProperties()
    System.setProperty("druid.mysql.usePingMethod","false");