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How to monitor the performance of an application in Java, I believe that many inexperienced people do not know what to do. Therefore, this paper summarizes the causes and solutions of the problem. Through this article, I hope you can solve this problem.

Parameter types of JVM

Standard parameter (Eg.)

-help

-server/-client

-version/-showversion

-cp/-classpath

X parameter (non-standardized parameter)

-Xint: interpreting and executing

-Xcomp: compile to native code the first time you use it

-Xmixed: mixed mode, where jvm decides whether or not to compile to native code

XX parameters (non-standard conversion parameters, relatively unstable, mainly used for JVM tuning and Debug)

Classification of XX parameters:

-Xmx/-Xms (actually the XX parameter) sets the maximum and minimum memory of JVM.-Xms is equivalent to-XX:InitialHeapSize,-Xmx is equivalent to-XX:MaxHeapSize.

-XX:+PrintFlagsInitial to view the initial values of JVM running parameters

-XX:+PrintFlagsFinal to view the final value of JVM running parameters (= for default value,: = for value modified by user or JVM)

-XX:+UnlockExperimentalVMOptions unlocking experimental parameters

-XX:+UnlockDiagnosticVMOptions unlock diagnostic parameters

-XX:+PrintCommandLineFlags print command line arguments

-XX:+HeapDumpOnOutOfMemoryError automatically Dump Heap Error when memory overflow occurs

-XX:HeapDumpPath=./ memory overflow HeapDump log,. / refers to the current running directory

Boolean type:-XX: [+ | -], for example:-XX:+UseConcMarkSweepGC

Non-Boolean type:-XX:= indicates that the value of the name attribute is value, for example:-XX:MaxGCPauseMillies=500

Jps

Jps can see all java processes by default

The-l parameter indicates that a specific Class is seen.

!!! All parameters need to be completed.

Jinfo

Jinfo-flag MaxHeapSize [pid] sees the value of the MaxHeapSize of the selected pid

Jinfo-flags [pid] sees all parameter values for the selected pid, both modified and unmodified

!!! All parameters need to be completed.

Jstat

Number of Loaded classes loaded

How many kBs are loaded by the Bytes class

Number of unloaded Unloaded classes

How many kBs has been uninstalled by the Bytes class

Total time spent loading and unloading Time classes

How many compilation tasks has Compiled completed (compiling a method to a local method)

Number of Failed compilation task failures

The number of times the Invalid compilation task is invalid

Total compilation time of Time

The compilation type of the last compilation failure of FailedType

The name of the class or method that failed in the last compilation of FailedMethod

Total amount and usage of S0C\ S1C\ S0U\ S1U S0 and S1

Total amount and usage of EC\ EU Eden area

Total amount and usage of OC\ OU Old area

Total amount and usage of MC\ MU Metaspace zones

CCSC\ CCSU compress the total amount and usage of class space

The number and time of YGC\ YGCT YoungGC

The number and time of FGC\ FGCT FullGC

Total GC time of GCT

You can view the following information:

All options:

-class to view class loading information. The usage jstat-class [pid] [interval millseconds] [count] represents the class loading information of pid that prints count times at intervals of interval milliseconds:

-compiler views JIT compilation information. Jstat-compiler [pid] [interval millseconds] [count] represents the JIT compilation information of pid that prints count times at intervals of interval milliseconds:

-gc to view garbage collection information. The usage jstat-gc [pid] [interval millseconds] [count] represents the gc information of pid that prints count times at intervals of interval milliseconds:

-gcutil

-gccause

-gcnew

-gcold

-printcompilation

!!! All parameters need to be completed.

Class loading information

Garbage collection information

JIT compilation information

Memory structure of JVM

Stack area: Young area (Servival area [S0+S1] + Eden area) + Old area. S0 and S1 are the same size. At the same time, S0 and S1 will only enable one.

Non-heap area (Metaspace): the local memory of the operating system, CCS area (exists after short pointers are enabled) + CodeCache area (where JIT code information is stored, and JNI code information is also here)

How to locate the memory overflow problem

Construct a memory overflow, for example, set-Xmx32M-Xms32M, construct a heap memory overflow, which only needs a constant new object; set-XX:MetaspaceSize=32M-XX:MaxMetaspaceSize=32M to construct a non-heap memory overflow, such as using less ASM to construct a Class file.

The difference between memory overflows

C++ memory overflow mainly refers to the loss of memory pointers, while Java memory overflow mainly refers to the non-release of objects that have been occupied.

Jmap

-dump: options have: live- only exports surviving objects, format=b- exports binary format, and file= represents the exported file.

You can export Heap logs manually

After reading the above, have you mastered how to monitor the performance of an application in Java? 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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