今天，公司项目某个模块的导出报如下错误：
HTTP Status 500 – Internal Server Error Type Exception Report Message Handler dispatch failed; nested exception is java.lang.OutOfMemoryError: GC overhead limit exceeded Description The server encountered an unexpected condition that prevented it from fulfilling the request. Exception org.springframework.web.util.NestedServletException: Handler dispatch failed; nested exception is java.lang.OutOfMemoryError: GC overhead limit exceeded org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1006) org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:925) org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:978) org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:881) javax.servlet.http.HttpServlet.service(HttpServlet.java:661) org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:855) javax.servlet.http.HttpServlet.service(HttpServlet.java:742) org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:61) org.apache.shiro.web.servlet.AdviceFilter.executeChain(AdviceFilter.java:108) org.apache.shiro.web.servlet.AdviceFilter.doFilterInternal(AdviceFilter.java:137) org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125) org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:66) org.apache.shiro.web.servlet.AbstractShiroFilter.executeChain(AbstractShiroFilter.java:449) org.apache.shiro.web.servlet.AbstractShiroFilter$1.call(AbstractShiroFilter.java:365) org.apache.shiro.subject.support.SubjectCallable.doCall(SubjectCallable.java:90) org.apache.shiro.subject.support.SubjectCallable.call(SubjectCallable.java:83) org.apache.shiro.subject.support.DelegatingSubject.execute(DelegatingSubject.java:387) org.apache.shiro.web.servlet.AbstractShiroFilter.doFilterInternal(AbstractShiroFilter.java:362) org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125) org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:357) org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:270) com.thetransactioncompany.cors.CORSFilter.doFilter(CORSFilter.java:209) com.thetransactioncompany.cors.CORSFilter.doFilter(CORSFilter.java:244) org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) Root Cause java.lang.OutOfMemoryError: GC overhead limit exceeded java.util.Arrays.copyOf(Arrays.java:3332) java.lang.AbstractStringBuilder.ensureCapacityInternal(AbstractStringBuilder.java:124) java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:448) java.lang.StringBuilder.append(StringBuilder.java:136) org.apache.ibatis.executor.resultset.ResultSetWrapper.getMapKey(ResultSetWrapper.java:176) org.apache.ibatis.executor.resultset.ResultSetWrapper.getMappedColumnNames(ResultSetWrapper.java:158) org.apache.ibatis.executor.resultset.DefaultResultSetHandler.applyPropertyMappings(DefaultResultSetHandler.java:428) org.apache.ibatis.executor.resultset.DefaultResultSetHandler.getRowValue(DefaultResultSetHandler.java:916) org.apache.ibatis.executor.resultset.DefaultResultSetHandler.applyNestedResultMappings(DefaultResultSetHandler.java:963) org.apache.ibatis.executor.resultset.DefaultResultSetHandler.getRowValue(DefaultResultSetHandler.java:918) org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleRowValuesForNestedResultMap(DefaultResultSetHandler.java:881) org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleRowValues(DefaultResultSetHandler.java:328) org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleResultSet(DefaultResultSetHandler.java:303) org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleResultSets(DefaultResultSetHandler.java:196) org.apache.ibatis.executor.statement.PreparedStatementHandler.query(PreparedStatementHandler.java:64) org.apache.ibatis.executor.statement.RoutingStatementHandler.query(RoutingStatementHandler.java:79) sun.reflect.GeneratedMethodAccessor370.invoke(Unknown Source) sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) java.lang.reflect.Method.invoke(Method.java:498) org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:63) com.sun.proxy.$Proxy1141.query(Unknown Source) org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:63) org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:326) org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:156) org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:109) org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:83) sun.reflect.GeneratedMethodAccessor369.invoke(Unknown Source) sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) java.lang.reflect.Method.invoke(Method.java:498) org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:63) com.sun.proxy.$Proxy1140.query(Unknown Source) org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:148) org.springframework.remoting.support.RemoteInvocationUtils.fillInClientStackTraceIfPossible(RemoteInvocationUtils.java:45) org.springframework.remoting.support.RemoteInvocationResult.recreate(RemoteInvocationResult.java:156) org.springframework.remoting.support.RemoteInvocationBasedAccessor.recreateRemoteInvocationResult(RemoteInvocationBasedAccessor.java:85) org.springframework.remoting.httpinvoker.HttpInvokerClientInterceptor.invoke(HttpInvokerClientInterceptor.java:162) org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:185) org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:212) com.sun.proxy.$Proxy765.listInvoiceDetail(Unknown Source) com.csw.purchase.controller.InvoiceQueryController.exportAll(InvoiceQueryController.java:174) com.csw.purchase.controller.InvoiceQueryController$$FastClassBySpringCGLIB$$f1d52ef0.invoke(<generated>) org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204) org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:747) org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163) org.apache.shiro.spring.security.interceptor.AopAllianceAnnotationsAuthorizingMethodInterceptor$1.proceed(AopAllianceAnnotationsAuthorizingMethodInterceptor.java:82) org.apache.shiro.authz.aop.AuthorizingMethodInterceptor.invoke(AuthorizingMethodInterceptor.java:39) org.apache.shiro.spring.security.interceptor.AopAllianceAnnotationsAuthorizingMethodInterceptor.invoke(AopAllianceAnnotationsAuthorizingMethodInterceptor.java:115) org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:185) org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:689) com.csw.purchase.controller.InvoiceQueryController$$EnhancerBySpringCGLIB$$b3090726.exportAll(<generated>) sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) java.lang.reflect.Method.invoke(Method.java:498) org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:209) org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136) org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:102) org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:870) org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:776) org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:991) org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:925) org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:978) org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:881) javax.servlet.http.HttpServlet.service(HttpServlet.java:661) org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:855) javax.servlet.http.HttpServlet.service(HttpServlet.java:742) org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:61) org.apache.shiro.web.servlet.AdviceFilter.executeChain(AdviceFilter.java:108) org.apache.shiro.web.servlet.AdviceFilter.doFilterInternal(AdviceFilter.java:137) org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125) org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:66) org.apache.shiro.web.servlet.AbstractShiroFilter.executeChain(AbstractShiroFilter.java:449) org.apache.shiro.web.servlet.AbstractShiroFilter$1.call(AbstractShiroFilter.java:365) org.apache.shiro.subject.support.SubjectCallable.doCall(SubjectCallable.java:90) org.apache.shiro.subject.support.SubjectCallable.call(SubjectCallable.java:83) org.apache.shiro.subject.support.DelegatingSubject.execute(DelegatingSubject.java:387) org.apache.shiro.web.servlet.AbstractShiroFilter.doFilterInternal(AbstractShiroFilter.java:362) org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125) org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:357) org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:270) com.thetransactioncompany.cors.CORSFilter.doFilter(CORSFilter.java:209) com.thetransactioncompany.cors.CORSFilter.doFilter(CORSFilter.java:244) org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) Note The full stack trace of the root cause is available in the server logs. Apache Tomcat/8.5.24
内存溢出，导出前需要查询的sql如下：
SELECT pid.id, pid.materials_id, pid.invoice_id, pid.inform_order_detail_id, pid.unit_price, pid.invoice_amt, pid.remark, pid.biz_status, pid.version, pid.is_deleted, pid.create_user, pid.gmt_create, pid.create_user_id, pid.modified_user, pid.gmt_modified, pid.materials_release_id, m.id m_id, m.item_id m_item_id, m.code m_code, m.unit m_unit, m.name m_name, m.short_code m_short_code, m.primary_uom m_primary_uom, m.key_component_flag m_key_component_flag, m.materials_type m_materials_type, m.classification m_classification, m.is_examine m_is_examine, m.item_status m_item_status, m.is_examine_item m_is_examine_item, m.purchase_type m_purchase_type, m.gmt_modified m_gmt_modified, m.modified_user m_modified_user, iiod.id iiod_id, iiod.invoice_inform_order_id iiod_invoice_inform_order_id, iiod.materials_id iiod_materials_id, iiod.invoice_qty iiod_invoice_qty, iiod.unit_price iiod_unit_price, iiod.dispense_num iiod_dispense_num, iiod.package_deal_code iiod_package_deal_code, iiod.current_differ_price iiod_current_differ_price, i.id i_id, i.code i_code, i.supplier_id i_supplier_id, i.invoice_val i_invoice_val, i.old_code i_old_code, i.invoice_tax_val i_invoice_tax_val, i.tax_amount i_tax_amount, i.vmi_type i_vmi_type, i.invoice_abstract i_invoice_abstract, i.general_ledger_date i_general_ledger_date, i.input_time i_input_time, i.is_hand_dispose i_is_hand_dispose, i.invoice_status i_invoice_status, i.organization_id i_organization_id, i.invoice_type i_invoice_type, s.id s_id, s.name s_name, s.code s_code, s.short_code s_short_code, s.TYPE s_type, s.main_product s_main_product, s.tax_reg_num s_tax_reg_num, iio.id iio_id, iio.code iio_code, iio.end_date iio_end_date, iio.department_id iio_department_id, iio.supplier_id iio_supplier_id, iio.drawer iio_drawer, iio.vmi_type iio_vmi_type, iio.invoice_audit_status iio_invoice_audit_status, iio.organization_id iio_organization_id, iio.inform_order_type iio_inform_order_type, it.id it_id, it.invoice_id it_invoice_id, it.tax_rate it_tax_rate, it.tax_amount it_tax_amount FROM p_invoice_detail pid LEFT JOIN s_materials m ON pid.materials_id = m.id LEFT JOIN p_invoice_inform_order_detail iiod ON pid.inform_order_detail_id = iiod.id LEFT JOIN p_invoice_inform_order iio ON iiod.invoice_inform_order_id = iio.id LEFT JOIN p_invoice i ON pid.invoice_id = i.id LEFT JOIN p_invoice_tax it ON i.id = it.invoice_id LEFT JOIN s_supplier s ON s.id = i.supplier_id WHERE i.is_deleted = 0
其中表p_invoice_detail 中大概34W条数据，p_invoice_inform_order_detail中大概14W条数据，其它表中数据不超1W条，于是博主各种折腾，建索引，调整连接顺序等，都不起作用，博主用的navicat，每次查询我的naviicat就罢工，报unknown internal error (A70529121901) bad allocation，没办法，只好一个表一个表的排除，最后发现，左连接p_invoice_inform_order_detail 表后就会出现上述问题，其它表都没事，于是博主单独查询这张表发现也很慢：
用了37.704s只查询出8300条记录（表*有约14W条数据），但是同样的查询有34W条数据的表p_invoice_detail却用了12.640s就全部查询出来了，博主就奇怪了，于是一个字段一个字段的试，终于发现是表p_invoice_inform_order_detail中的dispose_num字段导致的，后来发现该字段为clob类型，问题定位就好说了，上网查询发现将clob字段转为string类型再查询出来会提高效率，于是照做：将最开始的iiod.dispense_num修改为dbms_lob.substr(iiod.dispense_num,dbms_lob.getlength(iiod.dispense_num),1) dispense_num：
SELECT pid.id, pid.materials_id, pid.invoice_id, pid.inform_order_detail_id, pid.unit_price, pid.invoice_amt, pid.remark, pid.biz_status, pid.version, pid.is_deleted, pid.create_user, pid.gmt_create, pid.create_user_id, pid.modified_user, pid.gmt_modified, pid.materials_release_id, m.id m_id, m.item_id m_item_id, m.code m_code, m.unit m_unit, m.name m_name, m.short_code m_short_code, m.primary_uom m_primary_uom, m.key_component_flag m_key_component_flag, m.materials_type m_materials_type, m.classification m_classification, m.is_examine m_is_examine, m.item_status m_item_status, m.is_examine_item m_is_examine_item, m.purchase_type m_purchase_type, m.gmt_modified m_gmt_modified, m.modified_user m_modified_user, iiod.id iiod_id, iiod.invoice_inform_order_id iiod_invoice_inform_order_id, iiod.materials_id iiod_materials_id, iiod.invoice_qty iiod_invoice_qty, iiod.unit_price iiod_unit_price, dbms_lob.substr(iiod.dispense_num,dbms_lob.getlength(iiod.dispense_num),1) dispense_num, iiod.package_deal_code iiod_package_deal_code, iiod.current_differ_price iiod_current_differ_price, i.id i_id, i.code i_code, i.supplier_id i_supplier_id, i.invoice_val i_invoice_val, i.old_code i_old_code, i.invoice_tax_val i_invoice_tax_val, i.tax_amount i_tax_amount, i.vmi_type i_vmi_type, i.invoice_abstract i_invoice_abstract, i.general_ledger_date i_general_ledger_date, i.input_time i_input_time, i.is_hand_dispose i_is_hand_dispose, i.invoice_status i_invoice_status, i.organization_id i_organization_id, i.invoice_type i_invoice_type, s.id s_id, s.name s_name, s.code s_code, s.short_code s_short_code, s.TYPE s_type, s.main_product s_main_product, s.tax_reg_num s_tax_reg_num, iio.id iio_id, iio.code iio_code, iio.end_date iio_end_date, iio.department_id iio_department_id, iio.supplier_id iio_supplier_id, iio.drawer iio_drawer, iio.vmi_type iio_vmi_type, iio.invoice_audit_status iio_invoice_audit_status, iio.organization_id iio_organization_id, iio.inform_order_type iio_inform_order_type, it.id it_id, it.invoice_id it_invoice_id, it.tax_rate it_tax_rate, it.tax_amount it_tax_amount FROM p_invoice_detail pid LEFT JOIN s_materials m ON pid.materials_id = m.id LEFT JOIN p_invoice_inform_order_detail iiod ON pid.inform_order_detail_id = iiod.id LEFT JOIN p_invoice_inform_order iio ON iiod.invoice_inform_order_id = iio.id LEFT JOIN p_invoice i ON pid.invoice_id = i.id LEFT JOIN p_invoice_tax it ON i.id = it.invoice_id LEFT JOIN s_supplier s ON s.id = i.supplier_id WHERE i.is_deleted = 0
修改后查询，发现还是很慢，于是将其它不需要的字段去掉，调整为：
SELECT i.id, i.gmt_create, i.code, i.invoice_tax_val, m.code materials_code, m.name materials_name, s.code supplier_code, s.name supplier_name, pid.unit_price, it.tax_rate, i.tax_amount, iiod.current_differ_price, pid.invoice_amt, i.invoice_val, pid.unit_price * pid.invoice_amt total_money, dbms_lob.substr(iiod.dispense_num,dbms_lob.getlength(iiod.dispense_num),1) dispense_num, decode(i.invoice_type,‘1‘,‘供应商平台‘,‘2‘,‘发票平台‘) FROM p_invoice_detail pid LEFT JOIN p_invoice i ON pid.invoice_id = i.id LEFT JOIN s_materials m ON pid.materials_id = m.id LEFT JOIN p_invoice_inform_order_detail iiod ON pid.inform_order_detail_id = iiod.id LEFT JOIN p_invoice_inform_order iio ON iiod.invoice_inform_order_id = iio.id LEFT JOIN p_invoice_tax it ON i.id = it.invoice_id LEFT JOIN s_supplier s ON s.id = i.supplier_id WHERE i.is_deleted = 0
这次总算不报错了，虽然查询单速度还是有点慢，但还能接受：
