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I am working on a Windows 2003 server (64-bit) with 8 GB RAM. How can I increase the heap memory maximum? I am using the -Xmx1500m flag to increase the heap size to 1500 Mb. Can I increase the heap memory to 75% of physical memory (6 GB Heap)?

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  • 7
    Have you tried -Xmx6g ? Did this not work? What did you observe? Commented Oct 14, 2009 at 10:14
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    I presume you tried increasing the heap but failed? Are you using a 64 bit JVM? Commented Oct 14, 2009 at 10:15
  • Thanks for comment but this is not working Commented Oct 14, 2009 at 14:21
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    Well - how do you know it isn't working? Does the JVM not start? Commented Oct 15, 2009 at 6:56
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    Just wanted to mention here that, starting from Java 8 It is now possible to set the heap memory as a fraction of the available memory with the options -XX:InitialRAMPercentage=percentage, -XX:MaxRAMPercentage=percentage and -XX:MinRAMPercentage=percentage, for more details check this stackoverflow.com/a/78161306/7586739 Commented Mar 14, 2024 at 14:52

14 Answers 14

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You can increase to 2GB on a 32 bit system. If you're on a 64 bit system you can go higher. No need to worry if you've chosen incorrectly, if you ask for 5g on a 32 bit system java will complain about an invalid value and quit.

As others have posted, use the cmd-line flags - e.g.

java -Xmx6g myprogram

You can get a full list (or a nearly full list, anyway) by typing java -X.

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13 Comments

It has been my experience that the actual heap size Java will accept using a 32b VM (on a 32b or 64b system -- the VM is the important part, here), is around 2G. Also, surprised asker did not first search and find: stackoverflow.com/questions/1596009/… and: stackoverflow.com/questions/37335/…
ah, you're right of course - on a 32 bit system you can only address 2 Gb of memory.
No. But people commonly do it because the JVM can never waste time resizing. Doubt that it matters much, TBH.
@PhilipRego you set it to whatever you want, up to the limits the JVM can address. -Xmx2G sets your memory to 2G (also look at -Xms). This doesn't say anything at all about how much memory your going to need.
JAVA_OPTS didn't work for me. JAVA_TOOL_OPTIONS did.
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It is possible to increase heap size allocated by the JVM by using these command line options:

-Xms<size> set initial Java heap size -Xmx<size> set maximum Java heap size -Xss<size> set java thread stack size

In the following example, minimum heap size is set to 16mb, and the maximum to 64mb:

java -Xms16m -Xmx64m ClassName
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35

On a 32-bit JVM, the largest heap size you can theoretically set is 4gb. To use a larger heap size, you need to use a 64-bit JVM. Try the following:

java -Xmx6144M -d64

The -d64 flag is important as this tells the JVM to run in 64-bit mode.

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Thank you boss but it is not working in my system there is some thing else I am missing
Define "not working". Does it not start and give you an error? Does it start but use a different heap size?
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You can increase the Heap Size by passing JVM parameters -Xms and -Xmx like below:

For Jar Files:

java -jar -Xms4096M -Xmx6144M jarFilePath.jar

For Java Files:

 java -Xms4096M -Xmx6144M ClassName

The above parameters increase the InitialHeapSize (-Xms) to 4GB (4096 MB) and MaxHeapSize(-Xmx) to 6GB (6144 MB).

But, the Young Generation Heap Size will remain same and the additional HeapSize will be added to the Old Generation Heap Size. To equalize the size of Young Gen Heap and Old Gen Heap, use -XX:NewRatio=1 -XX:-UseAdaptiveSizePolicy params.

java -jar -Xms4096M -Xmx6144M -XX:NewRatio=1 -XX:-UseAdaptiveSizePolicy pathToJarFile.jar

-XX:NewRatio = Old Gen Heap Size : Young Gen HeapSize (You can play with this ratio to get your desired ratio).

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15

It is possible to increase heap size allocated by the JVM in eclipse directly In eclipse IDE goto

Run---->Run Configurations---->Arguments

Enter -Xmx1g(It is used to set the max size like Xmx256m or Xmx1g...... m-->mb g--->gb)

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Just to add this should be a VM argument (eclipse gives you two options).
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java -d64 -Xms512m -Xmx4g HelloWorld

where, -d64: Will enable 64-bit JVM -Xms512m: Will set initial heap size as 512 MB -Xmx4g: Will set maximum heap size as 4 GB (here java file name is : HelloWorld.java)

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Please use below command to change heap size to 6GB

export JAVA_OPTS="-Xms6144m -Xmx6144m -XX:NewSize=256m -XX:MaxNewSize=356m -XX:PermSize=256m -XX:MaxPermSize=356m"
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If I have 8G memory in my system and I can see from task manager that alsways 70% of that is in use; is this possible to allocate 6G memory to java heap size?
@Reihan_amn Yes and no, if you exceed your memory it will go to paging, which is on the disk and incredibly slow. If you exceed the page files then you're in for a bad time.
If this export cmd is used.... then will any java program by default be limited to 6Gb unless -Xm* values are specified at the java call?
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Can I increase the heap memory to 75% of physical memory(6GB Heap).

Yes you can. In fact, you can increase to more than the amount of physical memory, if you want to.

Whether it is a good idea to do this depends on how much else is running on your system. In particular, if the "working set" of the applications and services that are currently running significantly exceeds the available physical memory, your system is liable to "thrash", spending a lot of time moving virtual memory pages to and from disk. The net effect is that the system gets horribly slow.

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Thanks for your comment But How can I increase.Plz can you give command.
Try -Xmx6000m. It ought to work if you are using a 64bit version of Java.
Are you sure that you are running a 64bit version of Java? On a 64bit operating system?
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Several people pointed out the specific answers for heap size with the jvm options of -Xms and -Xms. I want to point out that this is not the only type of memory options for the jvm. Specifically if you are get stack over flows, then you'll want to increase the size of the stack by adding an additional option like -Xss8m.

For this problem, the jvm options of something like -Xms2g -Xmx6g -Xss8m would be a solution.

I'm sharing this information as my google searches on how to increase jvm memory took me to this solution, and the solutions didn't work with high amounts of memory allocation. Once I figured out what the specific settings were for, I was able to google how to increase the stack size and found the missing param. :) Hope this saves others time, as it would of saved me a ton of time. :)

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Can I increase the heap memory to 75% of physical memory(6GB Heap).

I don't know why none of the answers mention this (probably because the question is old), but starting from Java 8, there are three dedicated JVM options to control the heap size as a fraction of the available memory, which are very useful, especially for containerized applications.

These options are:

-XX:InitialRAMPercentage=percent

The InitialRAMPercentage JVM parameter allows us to configure the initial heap size of the Java application. It’s a percentage of the total memory of a physical server or container.

-XX:MaxRAMPercentage=percent

The MaxRAMPercentage parameter allows setting the maximum heap size for a JVM running with a large amount of memory (greater than 200 MB).

This is the option that can be used for the case mentioned in the question:

-XX:MaxRAMPercentage=75

-XX:MinRAMPercentage=percent

Unlike its name, allows setting the maximum heap size for a JVM running with a small amount of memory (less than 200MB).

For more details, check out this article: https://www.baeldung.com/java-jvm-parameters-rampercentage.

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This only works with 64 bit version of Java. Go to Control Panel and click on the Java icon. On the small window of Java Control Panel, click on the Java menu bar and then click on view button.

If you have two Java platforms, disable the previous version of Java, then click on Runtime parameters text field and write -Xmx1024m or less than RAM size. Don't increase heap size equal to RAM otherwise your system will crash.

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If you make the heap size equal to RAM, the system will not crash. Instead, the system will start paging and get nice and slow.
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Yes. You Can.

You can increase your heap memory to 75% of physical memory (6 GB Heap) or higher.

Since You are using 64bit you can increase your heap size to your desired amount. In Case you are using 32bit it is limited to 4GB.

$ java -Xms512m -Xmx6144m JavaApplication

Sets you with initial heap size to 512mb and maximum heapsize to 6GB.

Hope it Helps.. :)

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1 Comment

This seems very similar to the two top-voted answers posted a few years earlier.
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I have problem running the py files in my java code using eclipse/STS, getting PyException due to insufficient jvm heap memory. I have done the changes as mentioned below and I'm able to resolve this issue. Below is my System configuration.

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And these are the changes I did in my workspace and voila it runs perfect now.

enter image description here enter image description here

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Here are the steps if someone wants to know how to do this in windows.

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