On Windows, you can use the following command to find out the defaults on the system where your applications runs.
java -XX:+PrintFlagsFinal -version | findstr HeapSize
Look for the options MaxHeapSize (for -Xmx) and InitialHeapSize for -Xms.
On a Unix/Linux system, you can do
java -XX:+PrintFlagsFinal -version | grep HeapSize
I believe the resulting output is in bytes.
Answer from stones333 on Stack OverflowOn Windows, you can use the following command to find out the defaults on the system where your applications runs.
java -XX:+PrintFlagsFinal -version | findstr HeapSize
Look for the options MaxHeapSize (for -Xmx) and InitialHeapSize for -Xms.
On a Unix/Linux system, you can do
java -XX:+PrintFlagsFinal -version | grep HeapSize
I believe the resulting output is in bytes.
For Java SE 5: According to Garbage Collector Ergonomics [Oracle]:
initial heap size:
Larger of 1/64th of the machine's physical memory on the machine or some reasonable minimum. Before J2SE 5.0, the default initial heap size was a reasonable minimum, which varies by platform. You can override this default using the -Xms command-line option.
maximum heap size:
Smaller of 1/4th of the physical memory or 1GB. Before J2SE 5.0, the default maximum heap size was 64MB. You can override this default using the -Xmx command-line option.
UPDATE:
As pointed out by Tom Anderson in his comment, the above is for server-class machines. From Ergonomics in the 5.0 JavaTM Virtual Machine:
In the J2SE platform version 5.0 a class of machine referred to as a server-class machine has been defined as a machine with
- 2 or more physical processors
- 2 or more Gbytes of physical memory
with the exception of 32 bit platforms running a version of the Windows operating system. On all other platforms the default values are the same as the default values for version 1.4.2.
In the J2SE platform version 1.4.2 by default the following selections were made
- initial heap size of 4 Mbyte
- maximum heap size of 64 Mbyte
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JVM Heap optimization in newer Java versions is highly advanced and container-ready. This is great to quickly get an application in production without having to deal with various JVM heap related flags. But the default JVM heap and GC settings might surprise you. Know them before your first OOMKilled encounter.
Hi all... I have created a service in Java 21 using the latest springboot version 3.x.x series. When I deploy the service in live. I had allocated 2gb Ram and 1 Core Cpu for the pod. I was using internal cache that is EHCache, this tells why I have used 2gb Ram. After serving the requests for some time, the memory percentage of the pod had reached 95%, this was not expected as it was serving low numberiof requests. So I took a heap and analysed it. Below are the observations.
-
Used heap size is 113mb
-
Large memory object is EHCache 60mb (expected)
-
Unreferenced objects 400mb
-
GC algorithm used ( SerialGC) By taking heap dump I could not find much information. But what I observed is much memory objects were unreferenced objects. But GC should have cleared these. I saw online insstackoverflow, articles were telling most of them had faced same problem but did not post solutions to it. Many suggested to use different GC algorithm, so I ran the pod with G1GC algorithm. There was no significant observation seen. I am out of options now. Can somebody help me if they faced same issue and kindly post your solution. Thanks in Advance
Setup JAVA_OPTS as a system variable with the following content:
JAVA_OPTS="-Xms256m -Xmx512m"
After that in a command prompt run the following commands:
SET JAVA_OPTS="-Xms256m -Xmx512m"
This can be explained as follows:
- allocate at minimum 256MBs of heap
- allocate at maximum 512MBs of heap
These values should be changed according to application requirements.
EDIT:
You can also try adding it through the Environment Properties menu which can be found at:
- From the Desktop, right-click My Computer and click Properties.
- Click Advanced System Settings link in the left column.
- In the System Properties window click the Environment Variables button.
- Click New to add a new variable name and value.
- For variable name enter JAVA_OPTS for variable value enter -Xms256m -Xmx512m
- Click ok and close the System Properties Tab.
- Restart any java applications.
EDIT 2:
JAVA_OPTS is a system variable that stores various settings/configurations for your local Java Virtual Machine. By having JAVA_OPTS set as a system variable all applications running on top of the JVM will take their settings from this parameter.
To setup a system variable you have to complete the steps listed above from 1 to 4.
Try setting a Windows System Environment variable called _JAVA_OPTIONS with the heap size you want. Java should be able to find it and act accordingly.