Introduction
Memory is one of the important area in any application. Java has its own memory management. It is really important to efficiently maintain an optimum memory consumption and total run time in java. Failing to to do so will cause a lot of performance and other issues. Java handles its memory in two areas. Heap and Stack
Heap memory
All the objects created in a java application is stored in heap memory. We create an object using new operator. The garbage collector can logically separate the heap into different areas so that the GC is faster.
Stack memory
Stack is where the method invocations and the local variables are stored. If a method is called then its stack frame is put onto the top of the call stack. The stack frame holds the state of the method including which line of code is executing and the values of all local variables. The method at the top of the stack is always the current running method for that stack.
The maximum heap size and permgen size can be set during start up of java application using JVM parameters -Xmx and -XX:MaxPermSize
Memory leak
It is a type of resource leak when a program incorrectly manages memory allocations. That means a failure in a program to release the discarded memory which will cause impaired performance or failure.
OutOfMemory Errors
Java heap space error will be triggered when the application attempts to add more data into the heap space area, but there is not enough room for it.
Heap dump
A heap dump is a snapshot of the memory of a Java™ process. The snapshot contains information about the Java objects and classes in the heap at the moment the snapshot is triggered
Eclipse Memory Analyzer(MAT)
It is one of the feature rich heap analyzer that helps us analyse the heap memory. If we want look at a memory related issue, we need to generate the heap dumps during the issue and then analyse the same. Most of the heap issues will be resolved with a restart as it will freshen up the heap but it is just a temporary fix to retain the services. For permanent solution we need to perform a detailed analysis and fix the root cause.
1. Download the memory analyzer and extract the same. The source file can be obtained from below link
Memory analyzer download
2. Generate the heap dump file from the server.
The below pic says about the problem. It means the class loader has loaded an immense LRUCache object. We can now look at the application code and check when are these objects created and why the size is this huge.
This is an example of how to nail down root causes of memory issues using MAT.
The are options to look at Top components, Leakage suspects etc.We can also check the path to GC root, thread details, hash entries, duplicate classes and much more which can be explored our self.
Memory is one of the important area in any application. Java has its own memory management. It is really important to efficiently maintain an optimum memory consumption and total run time in java. Failing to to do so will cause a lot of performance and other issues. Java handles its memory in two areas. Heap and Stack
Heap memory
All the objects created in a java application is stored in heap memory. We create an object using new operator. The garbage collector can logically separate the heap into different areas so that the GC is faster.
Stack memory
Stack is where the method invocations and the local variables are stored. If a method is called then its stack frame is put onto the top of the call stack. The stack frame holds the state of the method including which line of code is executing and the values of all local variables. The method at the top of the stack is always the current running method for that stack.
The maximum heap size and permgen size can be set during start up of java application using JVM parameters -Xmx and -XX:MaxPermSize
Memory leak
It is a type of resource leak when a program incorrectly manages memory allocations. That means a failure in a program to release the discarded memory which will cause impaired performance or failure.
OutOfMemory Errors
Java heap space error will be triggered when the application attempts to add more data into the heap space area, but there is not enough room for it.
Heap dump
A heap dump is a snapshot of the memory of a Java™ process. The snapshot contains information about the Java objects and classes in the heap at the moment the snapshot is triggered
Eclipse Memory Analyzer(MAT)
It is one of the feature rich heap analyzer that helps us analyse the heap memory. If we want look at a memory related issue, we need to generate the heap dumps during the issue and then analyse the same. Most of the heap issues will be resolved with a restart as it will freshen up the heap but it is just a temporary fix to retain the services. For permanent solution we need to perform a detailed analysis and fix the root cause.
1. Download the memory analyzer and extract the same. The source file can be obtained from below link
Memory analyzer download
2. Generate the heap dump file from the server.
IBM generates the files with .phd format. It is not recognized by MAT. In order to analyse these files we need to add IBM Diagnostic Tool Framework for Java (DTFJ) plugin to it.
3. Adding DTFJ plugin to MAT
- Download the DTFJ assets from the below link DTFJ Source file
- Add DTFJ to MAT. Open MAT and choose Help->Install New Software
- In the dialog box click "Add" and provide the link. Follow the steps of the wizard.
- There are some case where the link does not work. The download the files manually(one by one from the above link) to a folder, select "Local" in Add dialog box and locate the folder.
- Restart MAT and you are good to go.
4. Choose File -> Open heap dump and locate your file. This will open the heap dump and it will automatically display the overview of the analysis.
Look at the overview and it will display the main problems if any or else there are multiple options available to analyze further.
Below is an example of a heap file where one object takes more than 75% of the memory. This shows that the object is not properly handled and hence we need to have a look at the cause behind such immense object creations.
The below pic says about the problem. It means the class loader has loaded an immense LRUCache object. We can now look at the application code and check when are these objects created and why the size is this huge.
This is an example of how to nail down root causes of memory issues using MAT.
The are options to look at Top components, Leakage suspects etc.We can also check the path to GC root, thread details, hash entries, duplicate classes and much more which can be explored our self.
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