springboot hikari数据库死链 出现异常

Posted 2022-05-31 QQ_851228082

最近系统间歇性很慢，比如登录，经常超时、无反应，查看log出现下述两种异常，
异常情况1

The last packet successfully received from the server was 995,202 milliseconds ago. The last packet sent successfully to the server was 995,202 milliseconds ago.
    at com.mysql.cj.jdbc.exceptions.SQLError.createCommunicationsException(SQLError.java:174)
    at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:64)
    at com.mysql.cj.jdbc.ConnectionImpl.setAutoCommit(ConnectionImpl.java:2056)
    at com.zaxxer.hikari.pool.ProxyConnection.setAutoCommit(ProxyConnection.java:388)
    at com.zaxxer.hikari.pool.HikariProxyConnection.setAutoCommit(HikariProxyConnection.java)
    at org.springframework.jdbc.datasource.DataSourceTransactionManager.doBegin(DataSourceTransactionManager.java:284)
    ... 44 common frames omitted

异常情况2

Caused by: java.sql.SQLNonTransientConnectionException: No operations allowed after connection closed.
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:110)
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97)
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:89)
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:63)
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:73)
    at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:73)
    at com.mysql.cj.jdbc.ConnectionImpl.setNetworkTimeout(ConnectionImpl.java:2490)
    at com.zaxxer.hikari.pool.PoolBase.setNetworkTimeout(PoolBase.java:550)
    at com.zaxxer.hikari.pool.PoolBase.isConnectionAlive(PoolBase.java:165)
    at com.zaxxer.hikari.pool.HikariPool.getConnection(HikariPool.java:179)
    ... 30 common frames omitted

怀疑数据库链接存在死链，后端是springboot使用的默认数据库连接池hikari，配置如下

spring:
  datasource:
    driver: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://x.x.x.x:3306/dbname?useUnicode=true&characterEncoding=utf-8
    username: xx
    password: xxxx
    hikari:
      maximumPoolSize: 20
      maxLifetime: 60000
      minimumIdle: 10
      connectionTestQuery: SELECT 'x'

查看源码得知，com.zaxxer.hikari.pool.HikariPool#getConnection(long)获取连接时，判断连接是否存活，

com.zaxxer.hikari.pool.PoolBase#isConnectionAlive
boolean isConnectionAlive(final Connection connection)
 
     try 
        setNetworkTimeout(connection, validationTimeout);

        final int validationSeconds = (int) Math.max(1000L, validationTimeout) / 1000;
        //如果不配置connectionTestQuery，才会使用jdbc校验机制
        if (isUseJdbc4Validation) 
           return connection.isValid(validationSeconds);
        
    

 com.zaxxer.hikari.pool.PoolBase#PoolBase
    PoolBase(final HikariConfig config)
   
      this.config = config;
      this.isUseJdbc4Validation = config.getConnectionTestQuery() == null;
     
   
   com.mysql.cj.jdbc.ConnectionImpl#isValid
   public boolean isValid(int timeout) throws SQLException 
        //发送心跳包
        pingInternal(false, timeout * 1000);
        return true;
        
    

继续往下跟到了com.mysql.cj.protocol.a.NativeProtocol#sendCommand

public final NativePacketPayload sendCommand(Message queryPacket, boolean skipCheck, int timeoutMillis) 
    //发送心跳包，debug得知发送的十六进制0x0e,也就是数字14
    send(queryPacket, queryPacket.getPosition());

总结

至此真相大白，因为配置了connectionTestQuery，所以没有使用jdbc的校验机制，修改方法就是去掉connectionTestQuery，jdbc的校验机制是在获取连接时，校验合法性，比定时校验效率要高；
另外，jdbc的校验相比上层库校验效率更高，因为是tcp层的心跳包而不是mysql引擎解析的sql语句，所以druid、hikari层的校验可以去掉了。

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