推荐链接：
总结——》【Java】
总结——》【Mysql】
总结——》【Redis】
总结——》【Kafka】
总结——》【Spring】
总结——》【SpringBoot】
总结——》【MyBatis、MyBatis-Plus】
总结——》【Linux】
总结——》【MongoDB】
总结——》【Elasticsearch】
解决——》CommunicationsException:Communications link failure
1、操作
正常查询数据库
2、现象
通信异常：通信链路故障
从服务器成功接收的最后一个数据包是66734毫秒前。最后一个成功发送到服务器的数据包是66732毫秒前。
2022-11-16 17:59:05.129 ERROR [10.122.139.93] [http-nio-8917-exec-9] [house-cms-0a7a8b5d-463497-1034] com.alibaba.druid.filter.logging.Slf4jLogFilter.statementLogError [line=149 ] : {conn-10020, pstmt-34465} execute error. SELECT id,title,dept_name,emp_code,emp_name,emp_phone,password,emp_mail,status,sort,type,remark,login_ip,login_time,is_delete,update_user,create_user,version,create_time,update_time FROM tb_user WHERE is_delete=0AND (emp_code = ?) limit 0,1com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failureThe last packet successfully received from the server was 66,734 milliseconds ago. The last packet sent successfully to the server was 66,732 milliseconds ago. at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) at java.lang.reflect.Constructor.newInstance(Constructor.java:423) at com.mysql.jdbc.Util.handleNewInstance(Util.java:425) at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:990) at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3562) at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3462) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3905) at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2530) at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2683) at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2495) at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1903) at com.mysql.jdbc.PreparedStatement.execute$original$Qo3qQCn7(PreparedStatement.java:1242) at com.mysql.jdbc.PreparedStatement.execute$original$Qo3qQCn7$accessor$m73OheMY(PreparedStatement.java) at com.mysql.jdbc.PreparedStatement$auxiliary$qLH27S5e.call(Unknown Source) at org.apache.skywalking.apm.agent.core.plugin.interceptor.enhance.InstMethodsInter.intercept(InstMethodsInter.java:86) at com.mysql.jdbc.PreparedStatement.execute(PreparedStatement.java) 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.wall.WallFilter.preparedStatement_execute(WallFilter.java:626) 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)3、原因
Mysql的连接等待时间（wait_timeout）默认8小时。在wait_timeout时间内，mysql的连接（connection）处于等待状态，一旦超过这个时间，mysql就会关闭。但是在我们的项目中的连接池中仍存在合法的connection，当你的程序需要再次访问数据库时，就会出现以上异常，但是再重新访问，又能正常从数据库中获取到数据。
# 连接等待时间，单位为秒# 默认8小时 = 28800s，windows最大24天，linux最大365天show global variables like 'wait_timeout';4、解决
1）执行sql调大wait_timeout的值
# mysql重启之后又会恢复成8小时set global wait_timeout=1814400;2）修改/etc/my.cnf调大wait_timeout的值
# 重启mysql服务之后生效，大约21天wait_timeout=1814400来源地址：https://blog.csdn.net/weixin_43453386/article/details/127907231
