【mysql】mysql数据库出现Communications link failure

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Java程序连接mysql数据库出现CommunicationsException: Communications link failure错误的问题，待继续整理补充TODO

问题

com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure

The last packet successfully received from the server was 31 milliseconds ago. The last packet sent successfully to the server was 36 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.ClientPreparedStatement.executeInternal(ClientPreparedStatement.java:953)
	at com.mysql.cj.jdbc.ClientPreparedStatement.execute(ClientPreparedStatement.java:370)
	at com.alibaba.druid.filter.FilterChainImpl.preparedStatement_execute(FilterChainImpl.java:3461)
	at com.alibaba.druid.filter.FilterEventAdapter.preparedStatement_execute(FilterEventAdapter.java:440)
	at com.alibaba.druid.filter.FilterChainImpl.preparedStatement_execute(FilterChainImpl.java:3459)
	at com.alibaba.druid.filter.FilterEventAdapter.preparedStatement_execute(FilterEventAdapter.java:440)
	at com.alibaba.druid.filter.FilterChainImpl.preparedStatement_execute(FilterChainImpl.java:3459)
	at com.alibaba.druid.proxy.jdbc.PreparedStatementProxyImpl.execute(PreparedStatementProxyImpl.java:167)
	at com.alibaba.druid.pool.DruidPooledPreparedStatement.execute(DruidPooledPreparedStatement.java:497)
	at org.apache.ibatis.executor.statement.PreparedStatementHandler.query(PreparedStatementHandler.java:64)
	at org.apache.ibatis.executor.statement.RoutingStatementHandler.query(RoutingStatementHandler.java:79)
	at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:63)
	at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:325)
	at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:156)
	at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:109)
	at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:89)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:151)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:145)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:140)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:135)

排查

有可能是由mysql数据库的配置引起的。mysql将其连接的等待时间(wait_timeout)缺省为8小时。在其客户程序中可以这样来查看其值： 28800 seconds，也就是8小时，如果在wait_timeout秒期间内，数据库连接(java.sql.Connection)一直处于等待状态，mysql就将该连接关闭。这时，你的Java应用的连接池仍然合法地持有该连接的引用。当用该连接来进行数据库操作时，就碰到上述错误。

mysql > show global variables like ‘wait_timeout’;

解决

1.mysql5以前的版本可以直接在jdbc连接url的配置中附加上“autoReconnect=true”。
2.将mysql的全局变量wait_timeout的值修改为最大。在文件my.ini的最后增加一行：wait_timeout=1814400

参考

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

将 Java 连接到 MySQL 数据库

解决Java程序连接mysql数据库出现CommunicationsException: Communications link failure错误的问题

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