[合集]JVM内存溢出问题的定位方法

淩亂°似流年 2022-10-10 11:18 127阅读 0赞

![ac12db74e0bf788f0de6e2e778bcbae1.png][]![072983065f742e1c769096a5747144c3.gif][]

戳这里，加关注哦～

今天给大家带来JVM体验之内存溢出问题的定位方法。  
废话不多说直接开始：

## 一、Java堆溢出 ##

测试代码如下：

import java.util.*;
    public class A {
        public static void main(String[] args) {
            List<String> strList = new ArrayList<>();
            while(true) {
                strList.add("");
            }
        }
    }

运行过程如下所示

![ddf9799a64550771bf764cdbc5bffa82.gif][]

我们在这里可以看到内存在不断的上涨，而Java在到一定时候会爆出OOM异常。  
如下:

> Exception in thread "main" java.lang.OutOfMemoryError: Java heap space  
> at java.util.Arrays.copyOf(Arrays.java:3210)  
> at java.util.Arrays.copyOf(Arrays.java:3181)  
> at java.util.ArrayList.grow(ArrayList.java:265)  
> at java.util.ArrayList.ensureExplicitCapacity(ArrayList.java:239)  
> at java.util.ArrayList.ensureCapacityInternal(ArrayList.java:231)  
> at java.util.ArrayList.add(ArrayList.java:462)  
> at A.A.main(A.java:9)
> 
> 现在程序是很简单，不过如果在大型项目里爆了堆溢出可就麻烦了。  
> 我们很难通过代码定位。  
> 所以我们需要用工具对其分析。

--------------------

## 二、堆内存快照 ##

我们先对Eclipse进行运行配置。

![2bf902e3bfc30d6ea5835f1e597bf8b9.png][]

![5439cce0fe62806d93e75824545313ec.png][]

参数如下所示  
`-XX:+HeapDumpOnOutOfMemoryError -Xms20m -Xmx20m`  
运行结果如下：

![b52a55ac1ca43d38136f1208190e0f03.png][]

随后我们找到项目地址，我们会发现在Project本目录中出现了个hprof文件

![8086ab94cb42580e8810a0550e749ddf.png][]

至此我们就把堆内存快照保存下来了。

--------------------

## 三、分析 ##

我们这里需要一个工具叫MAT是Eclipse提供的分析工具。  
![18e34548e2038a0b1eafdad2def5e8ac.png][]

这里是链接我们选择清华的镜像

https://mirrors.tuna.tsinghua.edu.cn/eclipse/mat/1.9.0/rcp/MemoryAnalyzer-1.9.0.20190605-win32.win32.x86\_64.zip

解压后运行  
![f7b4c06ae15ec808fd3f91cadef3b501.png][]这里运行会很慢，需要等待很久。打开后如下所示。  
![622f94f01024fcb37934dea012e1d45d.png][]

用这个工具把我们之前dump下来的东西放进去  
![0279c82af8451cdf2644cc1e644ec677.png][]

点开dominator\_tree，我们会发现问题储在main线程里，

![a865ba4a93f52c6136fe8dad403362d0.png][]这里有俩参数，一个是Shallow Heap,另一个是Retained Heap

<table> 
 <thead> 
  <tr> 
   <th>shallowHeap</th> 
   <th>Retained Heap</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>对象本身占用的内存大小</td> 
   <td>对象本身占用的大小+对象引用的大小总和</td> 
  </tr> 
 </tbody> 
</table>

常规理解就是如果我们对其做GC，那么就会释放掉这么大的内存。

而其中的这个Object对象就是我们之前创建的String类  
![da473dfdf3a9574b0caea158103c628d.png][]

## 至此我们就完成了对内存错误的定位。 ##

往期推荐

[JVM 调优后效果显著，性能提升了15%][JVM _15]

[Java 线程池配置的常见误区][Java]

[一篇文章让你搞懂如何通过Nginx来解决跨域问题][Nginx]

[一文让你理解什么是shallow heap及retained heap][shallow heap_retained heap]

[使用Eclipse Memory Analyzer Tool（MAT）分析线上故障(一)][Eclipse Memory Analyzer Tool_MAT]

[**java内存溢出问题分析过程二(附MAT超全操作文档)**][java_MAT]

[内存分析诊断系列-理解heap dump][-_heap dump]

[可视化界面在线生成JVM参数][JVM]

[Java 应用性能调优的一些实践][Java 1]

[分布式链路追踪工具pinpoint采样率原理分析][pinpoint]

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[JVM _15]: http://mp.weixin.qq.com/s?__biz=MzU2NDc4MjE2Ng%3D%3D&chksm=fc44e329cb336a3f97555b3a9e31adc0d9f5d8d34c6feae9d03587d536d35bc9bb6626465107&idx=1&mid=2247489040&scene=21&sn=bcf4b3d1f30d1dc2c9dc71e6a0b45aff#wechat_redirect
[Java]: http://mp.weixin.qq.com/s?__biz=MzU2NDc4MjE2Ng%3D%3D&chksm=fc44e26acb336b7ca018458fe2fe119ad3a201df0d6d716f1ce8dc5a5db79b70ec1b34c2841a&idx=1&mid=2247489363&scene=21&sn=b8db4cb36813b1864db8958b0e9257e9#wechat_redirect
[Nginx]: http://mp.weixin.qq.com/s?__biz=MzU2NDc4MjE2Ng%3D%3D&chksm=fc44e57fcb336c693c341a7ed329f5bf8e876fe794148d27e339684b1789079b1d1fd647b00d&idx=1&mid=2247487558&scene=21&sn=92bd8d1b9942701741c0fac01890ccb6#wechat_redirect
[shallow heap_retained heap]: http://mp.weixin.qq.com/s?__biz=MzU2NDc4MjE2Ng%3D%3D&chksm=fc44f78ecb337e98feb06bed690c03e8b2a1f847e960c9534cb2b5692a513f7b44dbba81c4fb&idx=1&mid=2247484087&scene=21&sn=fb317170339cfc9053ffb7c4e466ab1f#wechat_redirect
[Eclipse Memory Analyzer Tool_MAT]: http://mp.weixin.qq.com/s?__biz=MzU2NDc4MjE2Ng%3D%3D&chksm=fc44f7e8cb337efe3c8a0d65fdcad6021c841cd5c00c47e20b09ff7fa31470a29865cda12a0a&idx=1&mid=2247484113&scene=21&sn=2f603fec4d105d832db0783369b9fe57#wechat_redirect
[java_MAT]: http://mp.weixin.qq.com/s?__biz=MzU2NDc4MjE2Ng%3D%3D&chksm=fc44f7eccb337efa7e232d8649572010c07f32677556c590a5ad1da137e39f864377a52b1390&idx=1&mid=2247484117&scene=21&sn=8536a6b006352134c830b22fbe2a09ce#wechat_redirect
[-_heap dump]: http://mp.weixin.qq.com/s?__biz=MzU2NDc4MjE2Ng%3D%3D&chksm=fc44f794cb337e82fdcd6ad918d1a490d90908b6f453ddb45ad55b4a24a8b749e09baa9cc7a8&idx=1&mid=2247484077&scene=21&sn=5ae695faef094c78f2aa257b58b3034a#wechat_redirect
[JVM]: http://mp.weixin.qq.com/s?__biz=MzU2NDc4MjE2Ng%3D%3D&chksm=fc44f7e6cb337ef0bf114949eec1eb93e404f8ae64988a03cdc53a014119f496172a5de568f4&idx=1&mid=2247484127&scene=21&sn=92e774ee1edc2dd0013c60f1347d0fe6#wechat_redirect
[Java 1]: http://mp.weixin.qq.com/s?__biz=MzU2NDc4MjE2Ng%3D%3D&chksm=fc44f7dccb337ecadd6f748c4d5aae213003d3cc40c501d9865591e18539343083070888203b&idx=1&mid=2247484133&scene=21&sn=70156fc59563970321007d04a3d160b0#wechat_redirect
[pinpoint]: http://mp.weixin.qq.com/s?__biz=MzU2NDc4MjE2Ng%3D%3D&chksm=fc44f7d3cb337ec556bfe6aa2e48e32285cdc35ddc065bd65a50fbd3a0ac0915ba46c3834d46&idx=1&mid=2247484138&scene=21&sn=7a979a00666fdba5d9cd7fc7da3a5cfb#wechat_redirect
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