Eclipse virtual memory insufficiency Solution

Eclipse recently found that there are always insufficient virtual memory prompts in J2EE projects.
Root memory added two days ago.
To prevent me from having to write code that is annoying and out of memory
Don't let the broken machine get stuck again. Today, I found a solution. After trying, it seems I did not get out.
Insufficient memory prompt
The prompt is as follows:
Myeclipse has detected that less than 5% of the 64 MB of perm
Gen (non-heap memory) space remains. It is stronugly recommended
That you exit and restart myeclipse with new virtual machine memory
Paramters to increase this memory. Failure to do so can result in
Data loss. The recommended eclipse memory parameters are:
Eclipse.exe-vmargs-xms128m-xmx512m-XX: permsize = 64 m-XX: maxpermsize = 128 m

Solution:
Find the eclipse. ini configuration file under the eclipse Installation File
Usually it is written in-vmargs-Xms40m-Xmx256m
-Vmargs: Specifies the VM parameters.
-Xms40m: the virtual machine occupies the Minimum Memory of the system.
Xmx256m: the virtual machine occupies the maximum memory of the system.
-XX: permsize: Minimum heap size. When insufficient memory is reported, this is too small,
If the remaining heap space is less than 5%, a warning is reported. We recommend that you set this parameter slightly.
Larger, but it depends on the memory size of your machine.
-XX: permsize: Maximum heap size. This value is also larger.

Change the parameters in
-Vmargs
-Xms128m
-Xmx512m
-XX: permsize = 128 m
-XX: maxpermsize = 256 m

 

 

 

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If you do not set the memory, the following error occurs frequently when you use myeclipse: insufficient memory as shown in.

The prompt says: "myeclipse has detected that less than 5% of the 64 MB of perm Gen (non-heap memory) space remains. it means that only less than 5% of non-heap memory is idle currently. So we only need to set this value to a greater value.

The following parameters are provided in the prompt:

1. -Vmargs-xms128m-xmx512m-XX: permsize = 64 m-XX: maxpermsize = 128 m

There are several questions:
1. What are the meanings of each parameter?
2. Why can eclipse be started after I set-xmx and-XX: maxpermsize to 512m on some machines, but some machines cannot be started?
3. Why didn't eclipse execute the corresponding settings when writing the above parameters to the eclipse. ini file?

Let's answer them one by one.

1. What are the meanings of each parameter?

In the parameters-vmargs indicates setting JVM parameters, so the following are actually JVM parameters. First, let's take a look at the JVM memory management mechanism, and then explain the meaning of each parameter.

• Heap and non-heap memory
  According to the official statement: "A Java virtual machine has a heap. The heap is the runtime data area, and the memory of all class instances and arrays is allocated from this place. The heap is created when the Java Virtual Machine is started ." "Memory outside of the heap in JVM is called non-heap memory )". JVM manages two types of memory: heap and non-heap. In short, heap is the memory available for Java code and is reserved for developers. Non-heap is reserved for JVM, therefore, the method area, JVM internal processing or optimization of the required memory (such as the code cache after JIT compilation), each class structure (such as the runtime data pool, field and method data) the methods and constructor code are all in non-heap memory.
• Heap Memory Allocation
  The initial memory allocated by JVM is specified by-XMS. The default value is 1/64 of the physical memory. The maximum memory allocated by JVM is specified by-xmx. The default value is 1/4 of the physical memory. By default, when the free heap memory is less than 40%, the JVM will increase the heap until the maximum limit of-xmx. When the free heap memory is greater than 70%, the JVM will reduce the minimum limit of heap until-XMS. Therefore, the server generally sets-XMS and-xmx to be equal to each other to avoid adjusting the heap size after each GC.
• Non-heap memory allocation
  JVM uses-XX: permsize to set the non-heap memory initial value. The default value is 1/64 of the physical memory. The maximum non-heap memory size is set by XX: maxpermsize. The default value is 1/4 of the physical memory.
• JVM memory limit (maximum)
  First, JVM memory is limited to the actual maximum physical memory (nonsense! If the physical memory is infinitely large, the maximum JVM memory has a great relationship with the operating system. Simply put, although the 32-bit processor has a controllable memory space of 4 GB, the specific operating system will impose a limit, this limit is generally 2 GB-3 GB (1.5 GB-2 GB in windows and 2 GB-3 GB in Linux ), the 64-bit and above processors will not be limited.

2. Why can eclipse be started after I set-xmx and-XX: maxpermsize to 512m on some machines, but some machines cannot be started?

Through the introduction of JVM memory management, we have learned that JVM memory includes two types: heap memory and non-heap memory. In addition, the maximum JVM memory depends on the actual physical memory and operating system. Therefore, setting VM parameters causes program startup failure mainly due to the following reasons:

1) In the parameter, the value of-XMS is greater than-xmx, or the value of-XX: permsize is greater than-XX: maxpermsize;

2)-xmx value and-XX: The sum of maxpermsize exceeds the maximum JVM memory limit, such as the maximum memory limit of the current operating system or the actual physical memory. Speaking of the actual physical memory, it should be noted that if your memory is 1024 MB, but it is not likely to be 1024 MB in the actual system, because some of them are occupied by hardware.

3. Why didn't eclipse execute the corresponding settings when writing the above parameters to the eclipse. ini file?

Why is the same parameter valid in the shortcut or command line and invalid in the eclipse. ini file? This is because we have not followed the setting rules of the eclipse. ini file:

Parameters are in the form of "item value". If there is a space in the middle, you need to wrap it. If there is a space in the value, you need to include it in double quotation marks. For example, we use the-vm c:/Java/jre1.6.0/bin/javaw.exe parameter to set the virtual machine. In the eclipse. ini file, we need to write it as follows:

1. -VM
2. C:/Java/jre1.6.0/bin/javaw.exe

As mentioned above, the final parameter can be written in eclipse. ini as follows:

1. -Vmargs
2. -Xms128m
3. -Xmx512m
4. -XX: permsize = 64 m
5. -XX: maxpermsize = 128 m

The actual running result can be viewed through the "configuration details" button in the "help"-"about eclipse SDK" window in eclipse.

Note that the eclipse. ini file in the eclipse compressed package contains the following content:

1. -Showsplash
2. Org. Eclipse. Platform
3. -- Launcher. xxmaxpermsize
4. 256 m
5. -Vmargs
6. -Xms40m
7. -Xmx256m

Among them,-launcher. xxmaxpermsize (note that there are two connection lines at the top) and-XX: the meaning of maxpermsize.pdf is similar. I think the only difference is that the parameter set at startup of eclipse.exe, and the latter is the parameter in JVM used by eclipse. In fact, you can set one of the two, so here you can comment out-launcher. xxmaxpermsize and use # In the next line.