今天打开了前段时间写的个人博客系统，在查询文章内容的时候报了：Packet for query is too large (164,357 > 2,048). You can change this value on the server by setting the ‘max_allowed_packet’ variable.的错误。个人所使用的的数据库是mysql 5.1.36。搭建方式是在腾讯云服务器使用docker构建的。

以下就是报错信息：

### The error may exist in com/blog/mapper/ArticleBodyMapper.java (best guess)
### The error may involve defaultParameterMap
### The error occurred while setting parameters
### SQL: SELECT id,content,content_html AS contentHtml,article_id AS articleId FROM bl_article_body WHERE id=?
### Cause: com.mysql.cj.jdbc.exceptions.PacketTooBigException: Packet for query is too large (164,357 > 2,048). You can change this value on the server by setting the 'max_allowed_packet' variable.
; Packet for query is too large (164,357 > 2,048). You can change this value on the server by setting the 'max_allowed_packet' variable.; nested exception is com.mysql.cj.jdbc.exceptions.PacketTooBigException: Packet for query is too large (164,357 > 2,048). You can change this value on the server by setting the 'max_allowed_packet' variable.
	at org.springframework.jdbc.support.SQLStateSQLExceptionTranslator.doTranslate(SQLStateSQLExceptionTranslator.java:110)
	at org.springframework.jdbc.support.AbstractFallbackSQLExceptionTranslator.translate(AbstractFallbackSQLExceptionTranslator.java:70)
	at org.springframework.jdbc.support.AbstractFallbackSQLExceptionTranslator.translate(AbstractFallbackSQLExceptionTranslator.java:79)
	at org.springframework.jdbc.support.AbstractFallbackSQLExceptionTranslator.translate(AbstractFallbackSQLExceptionTranslator.java:79)
	at org.mybatis.spring.MyBatisExceptionTranslator.translateExceptionIfPossible(MyBatisExceptionTranslator.java:88)
	at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:440)
	at com.sun.proxy.$Proxy80.selectOne(Unknown Source)
	at org.mybatis.spring.SqlSessionTemplate.selectOne(SqlSessionTemplate.java:159)
	at com.baomidou.mybatisplus.core.override.MybatisMapperMethod.execute(MybatisMapperMethod.java:90)
	at com.baomidou.mybatisplus.core.override.MybatisMapperProxy$PlainMethodInvoker.invoke(MybatisMapperProxy.java:148)
	at com.baomidou.mybatisplus.core.override.MybatisMapperProxy.invoke(MybatisMapperProxy.java:89)
	at com.sun.proxy.$Proxy91.selectById(Unknown Source)
	at com.blog.service.impl.ArticleServiceImpl.findArticleBodyById(ArticleServiceImpl.java:252)
	at com.blog.service.impl.ArticleServiceImpl.copy(ArticleServiceImpl.java:241)
	at com.blog.service.impl.ArticleServiceImpl.findArticleById(ArticleServiceImpl.java:145)
	at com.blog.service.impl.ArticleServiceImpl$$FastClassBySpringCGLIB$$c2ea8815.invoke(<generated>)
	at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218)
	at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:688)
	at com.blog.service.impl.ArticleServiceImpl$$EnhancerBySpringCGLIB$$9251bd77.findArticleById(<generated>)
	at com.blog.controller.ArticleController.findArticleById(ArticleController.java:62)
	at com.blog.controller.ArticleController$$FastClassBySpringCGLIB$$b77ae0df.invoke(<generated>)
	at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218)
	at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:779)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163)
	at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:750)
	at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:97)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
	at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:750)
	at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:692)
	at com.blog.controller.ArticleController$$EnhancerBySpringCGLIB$$b0a364ad.findArticleById(<generated>)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205)
	at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:150)
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:117)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808)
	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1067)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:963)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)
	at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:909)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:681)
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:764)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:227)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
	at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
	at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:197)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:540)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:135)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:357)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:382)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:893)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1726)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
	at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191)
	at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.lang.Thread.run(Thread.java:745)
Caused by: com.mysql.cj.jdbc.exceptions.PacketTooBigException: Packet for query is too large (164,357 > 2,048). You can change this value on the server by setting the 'max_allowed_packet' variable.
	at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:107)
	at com.mysql.cj.jdbc.ClientPreparedStatement.executeInternal(ClientPreparedStatement.java:953)
	at com.mysql.cj.jdbc.ClientPreparedStatement.execute(ClientPreparedStatement.java:370)
	at com.zaxxer.hikari.pool.ProxyPreparedStatement.execute(ProxyPreparedStatement.java:44)
	at com.zaxxer.hikari.pool.HikariProxyPreparedStatement.execute(HikariProxyPreparedStatement.java)
	at sun.reflect.GeneratedMethodAccessor77.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.apache.ibatis.logging.jdbc.PreparedStatementLogger.invoke(PreparedStatementLogger.java:59)
	at com.sun.proxy.$Proxy131.execute(Unknown Source)
	at org.apache.ibatis.executor.statement.PreparedStatementHandler.query(PreparedStatementHandler.java:64)
	at org.apache.ibatis.executor.statement.RoutingStatementHandler.query(RoutingStatementHandler.java:79)
	at sun.reflect.GeneratedMethodAccessor76.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:63)
	at com.sun.proxy.$Proxy129.query(Unknown Source)
	at com.baomidou.mybatisplus.core.executor.MybatisSimpleExecutor.doQuery(MybatisSimpleExecutor.java:69)
	at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:325)
	at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:156)
	at com.baomidou.mybatisplus.core.executor.MybatisCachingExecutor.query(MybatisCachingExecutor.java:165)
	at com.baomidou.mybatisplus.extension.plugins.MybatisPlusInterceptor.intercept(MybatisPlusInterceptor.java:64)
	at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:61)
	at com.sun.proxy.$Proxy128.query(Unknown Source)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:147)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:140)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectOne(DefaultSqlSession.java:76)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:426)
	... 74 more

观察错误信息：发现是我要读取的数据量太大，让我通过设置“max_allowed_packet”变量在服务器上更改限制值。
接下来就是解决方法：
使用远程连接工具连接到数据库

然后重新设置 max_allowed_packet 大小 M是你要设置的大小
set global max_allowed_packet = M
使用命令：

show VARIABLES like '%max_allowed_packet%';

查看一下max_allowed_packet的默认大小；

在这里默认的大小是2048个字节，远远不够一篇文章的字节数：
接下来使用命令修改大小：

set global max_allowed_packet = 2*1024*1024*10;

修改成功之后，我们要重启mysql服务，在这里我用的是docker构建的mysql，所以我就重启docker的mysql的容器,重启之后，我们再连接到mysql数据库，使用命令：

show VARIABLES like '%max_allowed_packet%';

查看一下修改过后的max_allowed_packet 的大小

这样就完美的解决了这个报错。