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How to use VisualVM to analyze the performance of high concurrency projects, I believe that many inexperienced people are at a loss about this. Therefore, this paper summarizes the causes and solutions of the problem. Through this article, I hope you can solve this problem.

Before learning the knowledge of JVM, we generally need to use relevant parameters for analysis, and analysis generally requires some analysis tools, because we generally use IDEA, and VisualVM is also good for IDEA, so we choose VisualVM to analyze the performance of JVM. Here we introduce how to use VisualVM for performance analysis, and we need to know some principles of GC optimization and the purpose of GC optimization before analysis. And how to solve the problem when you encounter it.

Why do you need it?

It is hard to avoid memory leaks and performance bottlenecks in the process of developing large-scale Java applications, such as unreleased connections to files, networks and databases, unoptimized algorithms and so on. With the continuous operation of the application, the running efficiency of the whole system may be reduced, and in serious cases, the system will crash. In order to find out these hidden problems in the program, performance analysis tools are often used to analyze and optimize the performance of the application in the later stage of project development.

VisualVM is a free performance analysis tool. It obtains real-time data from the running time of the program through jvmstat, JMX, SA (Serviceability Agent), Attach API and other ways, so as to carry out dynamic performance analysis. At the same time, it can automatically select faster and lighter technologies to minimize the impact of performance analysis on applications and improve the accuracy of performance analysis.

2 how to install

There are two ways:

Did not follow the IDEA plug-in

If we don't follow the IDEA plug-in, we need to find the following execution program under the directory bin of JDK.

Then double-click execute, and the interface appears, as follows

However, we generally use IDEA, so we use plug-ins in the following way.

Follow the IDEA plug-in

First find the VisualVM installation in the plug-in

After installation, there will be two more VisualVM run buttons where it is running.

After running the program in this way, you can open the VisualVM program automatically.

3 basic introduction

This section starts with a brief introduction to the tool to see what basic features we will use.

When no other plug-ins are added, there are only a few features.

3.1 Overview

As shown in the figure above, the overview is basically a display of information such as our system properties, the JVM parameters set when running the program, and so on, so this section allows us to look at this information.

3.2 Monitorin

The ability to monitor this interface is useful, and you can see how cup is running, how the heap is being used, how the classes are, and how the threads are dynamic.

Therefore, we can use this interface to check whether cpu is good or not, and more importantly, we can check the usage of the heap, which is very important for us to analyze JVM.

3.3 Thread

As shown in the figure above, you can see that all threads are running, sleeping, waiting, residing, monitoring, and so on.

Note that none of the above is the key, but that there is another important feature in VisualVM that you can add plug-ins to get more functionality.

3.4 add plug-in

It is because of the extension of the plug-in that this tool is so powerful that VisualVM can do the following:

Displays the virtual machine process and its configuration, environment information, jps, jinfo.

Monitor the application's cpu, GC, heap, method area, and thread information (jstat, jstack).

Dump and analytics heap transfer storage snapshots (jmap, jhat).

There are many other functions.

Find the available plug-ins in tools-> and install them.

In the next section, we will analyze it using the installed plug-in Visual GC.

4 analyze the memory area of virtual machine by Visual GC

This section will use some of the basics of the Java virtual machine, so before you look at this section, please check out this article:.

This interface is divided into the following parts.

Space (Metaspace (metadata), Old Old Age, Cenozoic (Eden, S0, S1))

Graphs (Compile Time (compile time), Class Loader Time (class load time), GC Time (garbage collection time), Eden Space, Survivor 0, Survivor 1, Old Gen, Metaspace)

Histogram (Parameters parameter setting)

So after knowing these parameters, how to analyze whether the virtual machine is running well or bad? at this time, we need to know some basic optimization knowledge of the Java virtual machine.

First, you need to understand some principles of GC optimization.

Most Java applications do not require GC optimization on the server

Most Java applications that cause GC problems are not because of our wrong parameter settings, but because of code problems.

Before launching the application, consider setting the JVM parameters of the machine to the optimal (most suitable)

Reduce the number of objects created

Reduce the use of global variables and large objects

GC optimization is the last resort.

In practical use, analyzing the GC situation and optimizing the code is much more than optimizing the GC parameters.

In addition, we need to know the purpose of our GC optimization.

Minimize the number of objects transferred to the old era

Reduce the execution time of full GC

In general, we need to implement the following points

Reduce the use of global variables and large objects

Adjust the size of the new generation to the most appropriate

Set the size of the old age to be the most appropriate

Select the appropriate GC collector

As for how to calculate it, I will explain it through an example later.

In fact, if you want to know more about the principles of JVM memory allocation and recycling strategy, you can check out this article: how JVM memory allocation and recovery strategy works.

In general, after we have executed our program, the next step is to check the status of GC, and then analyze the results to determine whether optimization is needed.

Generally speaking, if the following targets are met, there is no need for GC.

The execution time of Minor GC is less than 50ms, and the execution of minor GC is infrequent, about once in 10 seconds.

Full GC execution time less than 1s full GC execution frequency is not frequent, not less than 10 minutes once

Example 1

Let's first look at an example where the GC state needs to be optimized. In this example, the maximum and minimum values we assign to the heap are 64m (very small heap size).

Analysis of GC State difference

/ * VM Args:-Xms64m-Xmx64m-XX:+HeapDumpOnOutOfMemoryError * @ author Ouyang Sihai * / public class HeapTest {static class StaticObject {} public static void main (String [] args) {List list = new ArrayList (); int I = 1; / / keep adding objects while (true) {list.add (new StaticObject ()) to the heap System.out.println (I); System.out.println (list.size ());}

The heap overflow occurs because the allocated heap memory is too small.

Then let's take a look at Visual GC's surveillance.

Monitor the interface

We can see from the use of the heap that it has basically been used up.

Visual GC surveillance

As can be seen from the above figure, in a short run time, Eden performed 49 GC times. Although the time is short, it shows that the space allocated by the new generation heap memory is too small, resulting in frequent GC.

At the same time, the old age of Old also carried out 33 times of GC, although the running time is also in the range that does not need to be optimized, and it can be seen from Survivor that there is basically no GC, indicating that these are large objects, which directly entered the old era of Old, resulting in frequent GC.

Therefore, what we need to optimize is to increase the size of the new and old heap memory while reducing the generation of large objects.

Parameter optimization analysis

Let's change the VM parameter to:-Xms512m-Xmx512m-Xmn128m-XX:+HeapDumpOnOutOfMemoryError and run for about 5 minutes to see the results again.

First, there is no heap memory overflow.

Monitor the situation

Heap memory has been increased, so there is no problem with heap memory.

Visual GC surveillance

After increasing the heap memory, the new generation of Eden has carried out 66 times of GC, and the usage time of 3.381s basically meets the requirements (less than 50ms of execution time of old minor GC is not frequent, about once in 10 seconds). At the same time, the old old has carried out two times of GC, and the use time is 4.127s, which still needs to be optimized and does not meet the optimization requirements.

Dump file analysis

Click the heap dump button to generate a dump file, and we can analyze some of the classes and objects.

After analysis, it is found that most of the StaticObject objects do not GC, and the problem is mainly here, so the next step needs to solve this problem.

Through the above analysis, we can show a problem, after increasing the heap memory, the GC situation of the new generation and the old era has been greatly improved, but there are still large object problems, so it still needs to be optimized.

Modify large objects for GC

Modify the program as follows:

/ * VM Args:-Xms512m-Xmx512m-Xmn128m-XX:+HeapDumpOnOutOfMemoryError * * @ author Ouyang Sihai * / public class HeapTest {/ * static class StaticObject {} * / public static void main (String [] args) {int I = 1; while (true) {ionization; System.out.println (I);}

Monitor the situation

The heap has been running well.

Visual GC surveillance

Compared with the last time, the situation in the old era has improved. Without GC, it means that the big object no longer exists.

Through the above analysis and optimization, we can meet the needs of GC, and there is no need for optimization.

After reading the above, have you mastered the method of using VisualVM to analyze the performance of highly concurrent projects? If you want to learn more skills or want to know more about it, you are welcome to follow the industry information channel, thank you for reading!

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