Eclipse. ini memory settings

Source: Internet
Author: User
Tags xms

-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 (HEAP) and non-heap (non-heap) memory
according to the official statement: "A Java virtual machine has a heap, And the heap is the data area during running hours, 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, the heap is the memory that Java Code can reach, 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 usage-XX: permsize: sets the non-heap memory initial value. The default value is 1/64 of the physical memory: maxpermsize sets the maximum non-heap memory size. 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 m 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 causesProgramThe following are the main reasons for failed startup:

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:

C: \ Java \ jre1.6.0 \ bin \ javaw.exe
As mentioned above, the final parameter can be written in eclipse. ini as follows:

-XX: permsize = 64 m
-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:

Org. Eclipse. Platform
-- Launcher. xxmaxpermsize
256 m
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.

3. Other startup parameters. If you have a dual-core CPU, you can try this parameter:

-XX: + useparallelgc

Enables faster GC execution. (Only the newly added GC parameters in JDK 5)



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