JVM visualvm: multi hop fault handling tool

VisualVM What is it? ？

    VisualVM（All-in-One Java Troubleshooting Tool） It is one of the most powerful operation monitoring and fault handling programs , It used to be... For a long time Oracle Official failure handling tools for virtual machines .

VisualVM What can be done ？

    VisualVM Can run monitoring 、 Troubleshooting , Other capabilities will also be provided , For example, performance analysis （Profiling）.VisualVM Compared with JProfiler、YourKit Etc. professional and charged Profiling Tools are no less than .

VIsualVM function

     Show virtual machine processes and process configuration 、 environmental information （jps、jinfo）.

· Monitor the application's processor 、 garbage collection 、 Pile up 、 Method area and thread information （jstat、jstack）.

·dump And analyze heap dump snapshot （jmap、jhat）.

· Method level program performance analysis , Find the most called 、 The longest way to run .

· Offline program snapshot ： Collect the runtime configuration of the program 、 Threads dump、 Memory dump Wait for the information to create a snapshot , You can send the snapshot to the developer Bug feedback .

· The unlimited possibilities of other plug-ins .

Download and install

https://visualvm.github.io/index.html

decompression

Get into etc open visualvm.conf

edit jdk Lu Jin , Your own jdk Lu Jin

function

Installing a plug-in

https://visualvm.github.io/pluginscenters.html

toos->plugins-> Change address

iy uj

Download plug-ins

Note that if it is a virtual machine, use the virtual machine to download

tools->Plugins->Downloaded

Import the plug-in and install, And on again VigualVM

If necessary, you can also install others

idea Installing a plug-in

Get into settings->plugins->Browse Repositories Search for ：VisualVM

Configure road force operation and jdk Catalog

Run selection

Related instructions ：

Pile up (Heap) ：JVM The managed memory is called heap

generational ： According to the life cycle of the object , Divide the heap into 3 Generations ：Young,Old and Permanent, Different collection algorithms are adopted according to the characteristics of different generations , Develop strengths and avoid weaknesses .

    Young（ The younger generation ）

The younger generation is divided into three sections . One Eden District , Two Survivor District . Most objects in Eden In the region . When Eden Area is full , Surviving objects will be copied to Survivor District （ One of the two ）, When this Survivor Area is full , The surviving object in this section will be copied to another Survivor District , When this Survivor When the district is full , From the first Survivor The copied object that is still alive at this time , Will be copied “ Years old (Tenured)”. We need to pay attention to ,Survivor The two regions are symmetric , It doesn't matter , So it's possible to have a slave in the same region at the same time Eden Copy the object , And the old one Survivor The copied object , And the only copy to the old area is from the first one Survivor The copied object . and ,Survivor One of the sections is always empty .

    Tenured（ The old generation ）

The old store objects that survive from the young . Generally speaking, the objects stored by the old generation are the objects with longer life span .

    Perm（ Lasting generation ）

For storing static files , Now Java class 、 Such method . Persistence has no significant effect on garbage collection , But some applications may dynamically generate or call some class, for example Hibernate etc. , In this case, you need to set up a large persistence generation space to store the newly added classes in the running process . Persistent generation size through -XX:MaxPermSize= Set it up .

    Metaspace（ Meta space ）

          With JDK8 The arrival of the ,JVM No more Perm. But the metadata information of the class （metadata） still , It's just that it's no longer stored in contiguous heap space , It's moving to something called “Metaspace” Local memory of （Native memory） in . The essence of meta space is similar to permanent generation , All right. JVM Implementation of method area in specification . But the biggest difference between Metaspace and permanent generation is ： The meta space is not in the virtual machine , It's using local memory .

Thread view

CPU see

Generate dump

Last

     use visualvm To analyze the performance of applications is also a very useful tool , Before the open source tools of cloud services and major platforms came out , This tool has always been treated as an artifact , Now, some of the analysis tools provided by major cloud services are more convenient 、 More efficient, so visualvm Although not the same as before, it is regarded as a requirement for performance analysis , But the value of this tool is still very high , Students in need can understand and master by themselves , Maybe this artifact will be used when upgrading to fight monsters .

Reference article ：

    https://blog.csdn.net/xlecho/article/details/103814673

    https://www.ibm.com/developerworks/cn/java/j-lo-visualvm/