Oom analysis tool mat

manufacture OOM

First, create it manually OOM scene

• take Java The memory of the process is smaller , Let the process as soon as possible OOM
• Set heap dump （ Stored as hprof file ）
• Set up hprof File save directory

produce OOM The code is attached at the end , Let's analyze it first and then look at the code .

analysis OOM reason

Import hprof file

File > Open Heap Dump… > choice hprof file , Here we mainly record the function and use of the five buttons in the red box , Basically, it is enough for us to find the location and cause of memory overflow .

Two intuitive main attributes

Shallow Heap： Shallow pile . That is, the heap memory occupied by the instance itself
Retained Heap： Reserved heap . That is, the relevant content of the instance （ Quotes ） Heap memory for

overview

The first interface we see after importing the file is overview

1. stay Detials We can see that OOM when ,jvm Memory occupied 、 Number of classes 、 The number of instances and the type of class loader .
2. The pie chart below shows the proportion of the largest instances , The description in the lower left corner also shows the information of the largest instance .
   In my example , The biggest example is …testclass.OOMCreater , Self size 8B , But related content （ quote ） But achieved 93.8 MB, Here we can guess , Should be OOMCreater There are more and more things inside this instance .

Histogram

Click on the histogram , according to Retained Heap Reverse order ：

Find the type that consumes the most memory , Right click > list objects > with income refrences, And then follow Retained Heap In reverse order ：

You can see that the instance in the first line occupies Probably 93MB Of memory .

Expand the reference level and find ：

1. Object Examples are ArrayList quote , The instance name is elementData
2. The list is again …OOMCreater Class instance reference , The instance name is test
3. …OOMCreater The instance of class is …Test Class instance reference , The instance name is creater

It can be inferred from this that ,…Test in …OOMCreater List elements in the instance of test Continuous filling leads to memory overflow .

Dominate the tree

We can also directly locate the type of exception through the domination tree ：

Directly to OOMCreater Medium test In the list elementData attribute , And all the contents in the list and memory occupation .

OQL

Can be like SQL Query the information of the specified class ：

then Right click > list objects > with income refrences

We see that this class is referenced in two places ：
One is what we found earlier …Test class
The other is ConcurrentHashMap, yes Sping Of Bean aggregate , among singletonObjetcs Indicates that this is a single example Bean.
stay table That's ok , We Right click > Java Colelctions > Hash Entries, You can see all in the container bean example ：

Thread Overview

There is OOM , We also need to know what he was doing .
Click the gear button , Find and produce OOM The thread of ：

1. Spring Project start
2. After the project starts , Called callRunner() Method , And performed the operation . Indicates that there is class inheritance SpringApplicationRunner Interface , Realization Spring Automatically execute a certain logic after startup .
3. Called in logic OOMCreater Medium addUuidStr() Method .
4. addUuidStr() Method will create UUID , Creating UUID A memory leak occurred in the process of , That is, there is not enough heap memory .

And then according to the information we got earlier ,OOMCreater Properties of test There are a lot of UUID Eventually led to memory leaks , It can be concluded that , It should be …Test Constantly calling …OOMCreater Example of addUuidStr() The consequences of the method .

Code that causes memory overflow

package com.dm.cloud.testclass;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.ApplicationArguments;
import org.springframework.boot.ApplicationRunner;
import org.springframework.context.annotation.Configuration;

@Configuration
public class Test implements ApplicationRunner {
    

    @Autowired
    private OOMCreater creater;

    @Override
    public void run(ApplicationArguments args) throws Exception {
    
        for(;;) {
    
            creater.addUuidStr();
        }
    }
}

package com.dm.cloud.testclass;

import org.springframework.stereotype.Component;

import java.util.ArrayList;
import java.util.List;
import java.util.UUID;

/** *  manufacture OOM */
@Component
public class OOMCreater {
    

    private List<String> test=  new ArrayList<>();

    public void addUuidStr(){
    
        String str = UUID.randomUUID().toString();
        test.add(str);
    }
}