Am I right in thinking that when one specifies VM arguments in an IDE (I'm using NetBeans in this instance), that these arguments are only passed when the code is run through the IDE itself?
Essentially, I'd like to specify that when my program runs, the VM's minimum/initial heap size is 2Gb. I can do this using the -Xms2048m command, but I'm wondering if there's some way to achieve this without having to type a command (for the customer's sake).
Even thought I set the VM argument in NetBeans, and Launch4J (I wrap the JAR into an EXE file), when the program boots & outputs the Runtime's total memory size, it always gives ~120Mb.
What am I missing?
Edit: I output the total memory size using...
int mb = 1024 * 1024;
System.out.println("Max Memory: " + Runtime.getRuntime().totalMemory() / mb);
Edit 2: Could one not create a initialising program that takes no arguments, but starts the main program with the relevant VM arguments? Something like...
public class Main {
public static void main(String[] args) {
String execName = new File(new File("").getAbsolutePath()) + "\\Program.exe";
Runtime rt = Runtime.getRuntime();
rt.exec("java -Xms2048m -Xmx4096m -jar " + execName);
}
}
The only way to do this is to have the program start another copy of the program witht eh heap you want. Note: the end user might not want 2 GB e.g.
If they have 32-bit windows they cannot e.g. if their default is only 120 MB, they most likely have a 32-bit windows client JVM which can't be 2 GB. If they have 32 GB or more they might want more than 2 GB.
BTW Gb = Giga-bit, Mb = Mega-bit, GB = Giga Byte. MB = Mega Byte.
No, You can't change the heap size programatically. Command line is the only way
Since the values must be set during JVM initialization,You cannot.
Some Useful discussion on the same on oracle forums.
And on SO :programatically setting max java heap size
Heap is able to shrink after GC iteration if GC decides that there are too many unused heap space allocated. Maybe that is way after your application starts it shows you the same size each time.
And also -Xms seems to set initial size of heap, not minimum
C:\Users\AStybaev>java -X
...
-Xms<size> set initial Java heap size
...
Related
I am playing around with Java, parameter -Xms and class Runtime.
I see that JVM allocates about 15% of the memory that is available - regardless how much it is.
Runtime rt Runtime.getRuntime ();
long total = rt.totalMemory ()
long free = rt.freeMemory ();
That is the case if I start my programm with paramter
-Xms4000m
as well as with
-Xms90m
I see the difference of Xms in the result of totalMemory.
I understand the strategy of allocating more from the beginning to avoid expensive reallocation.
But I do not know if that is in place here AND how I can meter the real memory-consumption of my program.
If your're using the Oracle JVM, you can use the command line tool jmap or the GUI tool jvisualvm to measure the heap consumption of your Java program.
Get the PID of the application and you can use top command in the below way to print out the statistics.
top -b | grep PID
You can see how the memory is utilized over time.
public class Test {
public static void main(String[] args) {
long heapsize = Runtime.getRuntime().totalMemory();
System.out.println("heapsize is :: " + heapsize/(1024*1024));
}
}
The output is:
heapsize is :: 245
Does this mean my runtime has only 245M memory? My computer has 8GB memory. I doubt output this is correct, since the running of Eclipse alone will consume a lot more than 245M.
In Eclipse, I click Windows->Preferences->Java->Installed JREs, and set Default JVM arguments as follows:
-ea -Xms256m -Xmx4096M
Then run the test again. It still prints out the same number, 245. How could this happen?
Edited: from Java doc for Runtime.getRuntime().totalMemory():
Returns the total amount of memory in the Java virtual machine.
The value returned by this method may vary over time, depending on the
host environment.
Your program doesn't run in Eclipse's heap space. Eclipse spawns off a separate JVM for your program.
Runtime.totalMemory() does indeed return the current heap size.
The -Xms argument specifies the initial heap size. Java will expand if it cannot free up enough memory through garbage collection until it reaches the maximum, as set by -Xmx. At this point, the JVM will exit with an OutOfMemoryError.
Java memory management is a complex topic, involving garbage collection, moving objects from nursery to tenured space, etc.
Is there a minimum -Xmx setting for Oracle's JVM? It looks like -Xmx2M does provide the application with more than 2 MB of heap size, as the Java Memory MX bean tells me it allocates like 10 MB...
Is there a minimum under which the JVM silently ignores the Xmx setting?
If I run
public static void main(String[] args) {
System.out.println("Heap size is " + Runtime.getRuntime().totalMemory() / 100000 / 10.0 + " MB");
}
with -mx8m on Java 7 update 25 64-bit I get
Heap size is 8.0 MB
but if I run with -mx2m I get
Heap size is 3.2 MB
So it does appear you get slightly more heap than you asked for for very small sizes. However, even for a small mobile device I wouldn't be worrying about every last MB because the JVM itself is much larger (can be over 100 MB of shared memory, thread etc)
i.e. if you can't spare a few MB, you won't be able to run the JVM anyway.
For jvm to start minimum 2mb of heapsize is required. You can set heap size to 0 bytes, but jvm will not start.
And maximum heap size recommended is 1/4 of total ram.
I have to allocate space to an array int input[] depending on the configuration parameters height and width.
int input[]=new int[height * width]; //this is line no 538
One of the configurations has parameters height=8192 and width=8192. So the size of the array becomes 67108864. But when i do this i get OutOfMemoryError.
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
at Test.main(Test.java:538)
I have ran this program on eclipse as well as on cygwin but i am facing the same problem. I think this is not an error and not exception. How can i rectify this?
Since 8192 * 8192 * 4 = 256 M (integers are 4 bytes each), your matrix is using 256 MB of heap space by itself.
You can tell the JVM how much heap space should be available to your application. From running man java and looking through the nonstandard options:
-Xmxn
Specify the maximum size, in bytes, of the memory allocation
pool. This value must a multiple of 1024 greater than 2MB.
Append the letter k or K to indicate kilobytes, or m or M to
indicate megabytes. The default value is chosen at runtime
based on system configuration. For more information, see
HotSpot Ergonomics
Examples:
-Xmx83886080
-Xmx81920k
-Xmx80m
On Solaris 7 and Solaris 8 SPARC platforms, the upper limit for
this value is approximately 4000m minus overhead amounts. On
Solaris 2.6 and x86 platforms, the upper limit is approximately
2000m minus overhead amounts. On Linux platforms, the upper limit
is approximately 2000m minus overhead amounts.
To use this option, you would start your application with a command like
java -Xmxn1024m -jar foo.jar
In Eclipse, you can add command-line options as well. This page on eclipse.org describes how to add command-line arguments to a Java program. You should add the -Xmxn1024m (or some other sufficiently large heap specification) to the "VM arguments" section of the dialog shown on that site.
You probably have too little heap space to hold an array of the size you are targeting. You can increase the size of your heap with command line switches. For example, to set it to 256MB, include this switch:
-Xmx256m
If you multiply height * width * 4 (4 is the storage in bytes for an int) you can get a rough gauge of the amount of heap you will need, assuming the rest of the program does not need a significant amount. You will certainly need some more heap than that quick calculation suggests. Add maybe 20% extra, and try that out.
To get a better number than a rule-of-thumb calculation, you can look into heap profilers. There are several open source options:
http://java-source.net/open-source/profilers
See http://javarevisited.blogspot.com/2011/05/java-heap-space-memory-size-jvm.html for a good discussion of the heap in Java.
memory is not enough for your program, may be memory leak there.
you may try below,if not solve try to increase jmx value.
java -xmx1g -xms512m
Depends on how much heap the JVM has. If you run it on the command line try adding -Xmx512m. If you work in an IDE add it to the "Run" properties.
An int is 32 bits (i.e. 4 bytes). So your array requires 8192*8192*4 bytes. This comes out at 256MB.
Java called with default arguments has only 64MB of heap space.
To get a larger heap, call Java using the -Xmx argument (Maximum memory size).
e.g. java -Xmx300M
Increase your memory arguments for your Java process by adding this flag to increase the heap. You might need to play around to get the optimal size for the heap. This will set the "max" heap size. The default is probably really small. 64M is a common max size for many Java EE containers.
*Note I'm not saying this is exactly the size you'll need. Your unique case will dictate the size you'll need which you may need to experiment with.
-Xmx256M
What does mean "Maximum Heap Size = Unlimited" in a j2me device?
For example of device:
http://www.developer.nokia.com/Devices/Device_specifications/E71/
Can I increase the app's heap size ?
Heap Memory means in programming, an area of memory reserved for data that is created at runtime that is, when the program actually executes. In contrast, the stack is an area of memory used for data whose size can be determined when the program is compiled.
Java heap is the heap size allocated to JVM applications which takes care of the new objects being created. If the objects being created exceed the heap size, it will throw an error saying memoryOutof Bound
Java's default heap size limit is 128MB. If you need more than this, you should use the -Xms and -Xmx command line arguments when launching your program:
java -Xms -Xmx
We can also give like in this format also.format is : -mx256m..Sometimes it will show error if you are using
java -Xms -Xmx format..In that case use -mx256m this.value can be changed..