纯干货:线上出现fullGC次数很多的排查思路以及实践总结

叁歲伎倆 2021-09-10 05:56 754阅读 0赞

> 最近线上发布了一个版本，导致full gc次数忽然就上去了，虽然对线上业务造成的影响还不是很大，但是为了以防万一还是对这个问题做了相关排查。

## GC命令排查 ##

一开始还是从堆的变化开始:

# 查看每秒的堆发生的变化以及gc的次数
    jstat -gcutil pid 1000

**相关参数**:

*  `s0` : **Heap上的 Survivor space 0 区已使用空间的百分比**
 *  `s1` : **Heap上的 Survivor space 1 区已使用空间的百分比**
 *  `E` : **Heap上的 Eden space 区已使用空间的百分比**
 *  `O` : **Heap上的 Old space 区已使用空间的百分比**
 *  `P` : **Perm space 区已使用空间的百分比**
 *  `M`：元数据区使用比例
 *  `CCS`：压缩使用比例
 *  `YGC` : **从应用程序启动到采样时发生 Young GC 的次数**
 *  `YGCT` : **从应用程序启动到采样时 Young GC 所用的时间(单位秒) FGC — 从应用程序启动到采样时发生 Full GC 的次数**
 *  `FGCT`\- **从应用程序启动到采样时 Full GC 所用的时间(单位秒) GCT — 从应用程序启动到采样时用于垃圾回收的总时间(单位秒)**

抓到了一个fullgc 升级的截图:

![6370985-2c4a90907ce3cf67.png][]

在这里插入图片描述

从这里发现在触发full gc的时候只有新生代的堆发生了明显的回收，但是老年代几乎没发生变化。

**所以不是老年代的内存不足导致的，然而第一感觉是会不会有大对象直接越过新生代直接到了老年代呢？但是现在想想应该也不太会，因为gc完之后老年代没有很明显的上升变化。**

既然这里看不出什么就开始另寻他路了。

## gc的日志分析： ##

GC参数 `建议线上都把这些日志打开`  
JVM的GC日志的主要参数包括如下几个：

-XX:+PrintGC # 输出GC日志
    -XX:+PrintGCDetails #输出GC的详细日志
    -XX:+PrintGCTimeStamps #输出GC的时间戳（以基准时间的形式）
    -XX:+PrintGCDateStamps #输出GC的时间戳（以日期的形式，如 2017-09-04T21:53:59.234+0800）
    -XX:+PrintHeapAtGC #在进行GC的前后打印出堆的信息
    -Xloggc:../logs/gc.log #日志文件的输出路径

拿到gc日志一行行看太麻烦了，这里推荐一个在线分析gc日志的神器：

### [gceasy][] ###

从线上拿到日志之后，上传到该网站，就会得到很多可视化的结果。

#### 堆的分配情况 ####

![6370985-ad4a1ab00e115f72][]

在这里插入图片描述

#### GC时间的区域划分 ####

![6370985-d936ea6ee2979864][]

在这里插入图片描述

这里可以看到:

*  最大的一次gc时间超过了1秒钟，平均的时间都在35ms之间。
 *  大部分时间都是在1秒以内,只有2次gc时间超过1秒。

#### GC前后的可视化图 ####

![6370985-95bc590d055e3633][]

在这里插入图片描述

红色的代表full gc时候的堆大小，都没有超过300M。  
minorgc是挺多,但是都在堆接近满了的情况。

#### GC停顿的情况 ####

![6370985-a7c68ac1356fa67b][]

在这里插入图片描述

我们这里比较关注full gc在198次，停顿时间在1分钟左右，每8分钟的样子就会触发一次。

#### GC触发的原因 ####

![6370985-6f9059e11eec38d9][]

在这里插入图片描述

这个图里面包含了很多关键的信息：

*  System.gc()触发的总数过多，达到300+次。
 *  其他的都是空间分配不足导致的gc，但是大部分是minor gc 这个是可以接受的。

得到上面的信息可以发现绝大部分的full gc引发的原因就是`System.gc()` 导致的，至于为什么超过300次？明明不是198次吗？稍后解答.

## 到底是哪里调用了System.gc? ##

这个是个很尴尬的问题，有可能是框架，也有可能是业务代码中。

想了解这个原因的时候联想到了阿里开源的[arthas][]

神器啊!

他有个功能能够在不重启的应用和改代码的情况下，对指定的方法进行拦截。  
**不说了，开干！**

### 启动 ###

curl -O https://alibaba.github.io/arthas/arthas-boot.jar
    java -jar arthas-boot.jar

### 开启安全方法拦截 ###

[arthas@18792]$ options unsafe true
     NAME    BEFORE-VALUE  AFTER-VALUE                                                                                                                                                                               
    -----------------------------------                                                                                                                                                                              
     unsafe  false         true

### 拦截指定的方法 ###

[arthas@18792]$ stack java.lang.System gc
    Press Q or Ctrl+C to abort.
    Affect(class-cnt:1 , method-cnt:1) cost in 277 ms 
    # 然后安静的等待调用出现吧!!!!!

**然后安静的等待调用出现吧!!!!!**

我这里贴一个我拦截的结果:

ts=2020-03-16 19:30:09;thread_name=http-nio-5314-exec-26;id=102;is_daemon=true;priority=5;TCCL=org.springframework.boot.context.embedded.tomcat.TomcatEmbeddedWebappClassLoader@781d050
        @java.lang.System.gc()
            at com.elab.core.utils.DateUtils.stringToDate(DateUtils.java:358)
            at com.elab.marketing.auth.service.impl.AdviserDispatchImpl.dispatch(AdviserDispatchImpl.java:162)
            at com.elab.marketing.auth.service.impl.AdviserDispatchImpl.dispatch(AdviserDispatchImpl.java:86)
            at com.elab.marketing.auth.service.impl.AdviserDispatchImpl$$FastClassBySpringCGLIB$$d0a51ab4.invoke(<generated>:-1)
            at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
            at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:738)
            at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)
            at org.springframework.aop.framework.adapter.MethodBeforeAdviceInterceptor.invoke(MethodBeforeAdviceInterceptor.java:52)
            at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
            at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:85)
            at com.elab.log.asepct.CatAspect.aroundMethod(CatAspect.java:65)
            at com.elab.marketing.auth.config.aspect.ServiceAspectBean.around(ServiceAspectBean.java:47)
            at sun.reflect.GeneratedMethodAccessor172.invoke(null:-1)
            at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
            at java.lang.reflect.Method.invoke(Method.java:498)
            at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:629)
            at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:618)
            at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:70)
            at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
            at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92)
            at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
            at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:673)
            at com.elab.marketing.auth.service.impl.AdviserDispatchImpl$$EnhancerBySpringCGLIB$$6e910ff2.dispatch(<generated>:-1)
            at sun.reflect.NativeMethodAccessorImpl.invoke0(NativeMethodAccessorImpl.java:-2)
            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:133)
            at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:97)
            at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827)
            at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738)
            at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
            at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:967)
            at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:901)
            at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
            at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:872)
            at javax.servlet.http.HttpServlet.service(HttpServlet.java:661)
            at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
            at javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
            at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
            at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
            at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
            at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
            at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
            at org.springframework.boot.web.filter.ApplicationContextHeaderFilter.doFilterInternal(ApplicationContextHeaderFilter.java:55)
            at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
            at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
            at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
            at org.springframework.boot.actuate.trace.WebRequestTraceFilter.doFilterInternal(WebRequestTraceFilter.java:110)
            at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
            at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
            at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
            at com.elab.log.filter.CatHttpRequestFilter.doFilter(CatHttpRequestFilter.java:45)
            at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
            at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
            at com.elab.log.filter.HttpCatCrossFliter.doFilter(HttpCatCrossFliter.java:75)
            at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
            at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
            at com.alibaba.arms.filter.EagleEyeFilter.doFilter(EagleEyeFilter.java:24)
            at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
            at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
            at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197)
            at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
            at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
            at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
            at org.springframework.boot.actuate.autoconfigure.MetricsFilter.doFilterInternal(MetricsFilter.java:106)
            at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
            at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
            at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
            at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199)
            at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
            at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:504)
            at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
            at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
            at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
            at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
            at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803)
            at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
            at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:790)
            at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459)
            at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
            at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
            at java.lang.Thread.run(Thread.java:748)
    
    ts=2020-03-16 19:31:35;thread_name=http-nio-5314-exec-16;id=f6;is_daemon=true;priority=5;TCCL=org.springframework.boot.context.embedded.tomcat.TomcatEmbeddedWebappClassLoader@781d050
        @java.lang.System.gc()
            at com.elab.core.utils.DateUtils.stringToDate(DateUtils.java:358)
            at com.elab.marketing.auth.service.impl.AdviserDispatchImpl.dispatch(AdviserDispatchImpl.java:162)
            at com.elab.marketing.auth.service.impl.AdviserDispatchImpl.dispatch(AdviserDispatchImpl.java:86)
            at com.elab.marketing.auth.service.impl.AdviserDispatchImpl$$FastClassBySpringCGLIB$$d0a51ab4.invoke(<generated>:-1)
            at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
            at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:738)
            at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)
            at org.springframework.aop.framework.adapter.MethodBeforeAdviceInterceptor.invoke(MethodBeforeAdviceInterceptor.java:52)
            at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
            at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:85)
            at com.elab.log.asepct.CatAspect.aroundMethod(CatAspect.java:65)
            at com.elab.marketing.auth.config.aspect.ServiceAspectBean.around(ServiceAspectBean.java:47)
            at sun.reflect.GeneratedMethodAccessor172.invoke(null:-1)
            at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
            at java.lang.reflect.Method.invoke(Method.java:498)
            at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:629)
            at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:618)
            at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:70)
            at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
            at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92)
            at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
            at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:673)
            at com.elab.marketing.auth.service.impl.AdviserDispatchImpl$$EnhancerBySpringCGLIB$$6e910ff2.dispatch(<generated>:-1)
            at sun.reflect.GeneratedMethodAccessor2519.invoke(null:-1)
            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:133)
            at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:97)
            at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827)
            at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738)
            at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
            at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:967)
            at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:901)
            at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
            at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:872)
            at javax.servlet.http.HttpServlet.service(HttpServlet.java:661)
            at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
            at javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
            at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
            at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
            at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
            at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
            at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
            at org.springframework.boot.web.filter.ApplicationContextHeaderFilter.doFilterInternal(ApplicationContextHeaderFilter.java:55)
            at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
            at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
            at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
            at org.springframework.boot.actuate.trace.WebRequestTraceFilter.doFilterInternal(WebRequestTraceFilter.java:110)
            at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
            at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
            at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
            at com.elab.log.filter.CatHttpRequestFilter.doFilter(CatHttpRequestFilter.java:45)
            at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
            at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
            at com.elab.log.filter.HttpCatCrossFliter.doFilter(HttpCatCrossFliter.java:75)
            at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
            at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
            at com.alibaba.arms.filter.EagleEyeFilter.doFilter(EagleEyeFilter.java:24)
            at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
            at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
            at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197)
            at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
            at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
            at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
            at org.springframework.boot.actuate.autoconfigure.MetricsFilter.doFilterInternal(MetricsFilter.java:106)
            at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
            at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
            at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
            at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199)
            at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
            at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:504)
            at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
            at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
            at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
            at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
            at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803)
            at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
            at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:790)
            at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459)
            at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
            at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
            at java.lang.Thread.run(Thread.java:748)

我这里出现了两次gc，根据链路去查看了相关源码，发现不知道是谁弄了一个工具类，try catch异常中加入的system.gc。**真让人头大**

具体代码:

/**
         * 将Date对象类型转化为指定的格式字符串
         *
         * @param date<Date>日期
         * @param format<String>格式
         * @return String
         */
        public static String dateToString(Date date, String format) {
    
            try {
                if(date!=null)
                    return new SimpleDateFormat(format).format(date);
            } catch (Exception e) {
                e.printStackTrace();
                System.gc();
            }
            return null;
        }

通过链路发现业务调用的时候还是个**for循环**，**所以会出现System.gc成双成对的触发......**

> 我猜也是为什么System.gc调用300+次数,但是fullgc只有198次，可能连续调用两次和一次没啥区别，但是仅仅只是猜测。很有可能是错误的，有知道的大佬可以指点一下。

不报异常不出现，坑死一堆程序员。

总结一下吧:

1.  出现异常可以先通过jstat、jmap等分析一下堆的情况，以及gc情况。
2.  通过分析gc日志可以快速定位gc触发的原因，以及堆的变化。
3.  如果是System.gc主动触发，可以通过阿里开源的arthas去拦截得到调用链。

虽然结果有点坑爹，但是思路是相通的。

如果有更好的思路以及实践

### 欢迎留言交流，共同学习。 ###

[6370985-2c4a90907ce3cf67.png]: /images/20210811/e5b99b915cf244d986bd9e60d59c760f.png
[gceasy]: https://links.jianshu.com/go?to=https%3A%2F%2Fwww.gceasy.io%2F
[6370985-ad4a1ab00e115f72]: /images/20210811/ae4ea2c3d43a4dea8aa97c4c50d88382.png
[6370985-d936ea6ee2979864]: /images/20210811/fb16629320cb4840b44520a55a2d6c04.png
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[arthas]: https://links.jianshu.com/go?to=https%3A%2F%2Fgithub.com%2Falibaba%2Farthas