MySQL中wait_timeout的坑
Posted ouzebo
tags:
篇首语:本文由小常识网(cha138.com)小编为大家整理,主要介绍了MySQL中wait_timeout的坑相关的知识,希望对你有一定的参考价值。
今天遇到了一个问题,一个项目,放到服务器(tomcat)下面的跑,但第二天,总是报错,项目还不能跑
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure The last packet successfully received from the server was 1 milliseconds ago. The last packet sent successfully to the server was 1 milliseconds ago. at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) at java.lang.reflect.Constructor.newInstance(Constructor.java:526) at com.mysql.jdbc.Util.handleNewInstance(Util.java:409) at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1127) at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3715) at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3604) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4155) at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2615) at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2776) at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2838) at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2082) at com.mysql.jdbc.PreparedStatement.execute(PreparedStatement.java:1307) at com.alibaba.druid.filter.FilterChainImpl.preparedStatement_execute(FilterChainImpl.java:2931) at com.alibaba.druid.filter.FilterEventAdapter.preparedStatement_execute(FilterEventAdapter.java:440) at com.alibaba.druid.filter.FilterChainImpl.preparedStatement_execute(FilterChainImpl.java:2929) at com.alibaba.druid.proxy.jdbc.PreparedStatementProxyImpl.execute(PreparedStatementProxyImpl.java:131) at com.alibaba.druid.pool.DruidPooledPreparedStatement.execute(DruidPooledPreparedStatement.java:493) at org.apache.ibatis.executor.statement.PreparedStatementHandler.query(PreparedStatementHandler.java:59) at org.apache.ibatis.executor.statement.RoutingStatementHandler.query(RoutingStatementHandler.java:73) at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:60) at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:267) at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:137) at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:96) at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:77) at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:108) at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:102) at org.activiti.engine.impl.db.DbSqlSession.selectListWithRawParameter(DbSqlSession.java:443) at org.activiti.engine.impl.db.DbSqlSession.selectList(DbSqlSession.java:434)
.......
发现这个问题是MySQL的坑:
wait_timeout的作用是,设置非交互连接(就是指那些连接池方式、非客户端方式连接的)的超时时间,默认是28800,就是8小时,超过这个时间,mysql服务器会主动切断那些已经连接的,但是状态是sleep的连接。而我们后端程序是运行在windows下的,所以安装的myodbc,并使用ado方式连接的,也就是连接池方式,这种方式的坏处是,当服务器端去连接mysql的时候,连接池里的连接已经被mysql主动断开,这时取回的连接就是null,再加上程序里对此没有做判断的话,接下来的对数据库的一系列的操作都会出现问题。
解决方案:
《1》增加 MySQL 的 wait_timeout 属性的值 (不推荐)
修改mysql安装目录下的配置文件 my.ini文件,这两个参数的默认值是8小时(60*60*8=28800)
wait_timeout=1814400
interactive_timeout=1814400
《2》减少连接池内连接的生存周期
减少连接池内连接的生存周期,使之小于上一项中所设置的wait_timeout 的值。修改 c3p0 的配置文件,在 Spring 的配置文件中设置:
<bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
<property name="maxIdleTime"value="1800"/>
<!--other properties -->
</bean>
《3》定期使用连接池内的连接
定期使用连接池内的连接,使得它们不会因为闲置超时而被 MySQL 断开。修改 c3p0 的配置文件,在 Spring 的配置文件中设置:
<bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
<property name="preferredTestQuery" value="SELECT 1"/>
<property name="idleConnectionTestPeriod" value="18000"/>
<property name="testConnectionOnCheckout" value="true"/>
</bean>
以上是关于MySQL中wait_timeout的坑的主要内容,如果未能解决你的问题,请参考以下文章