I am getting:
java.lang.OutOfMemoryError : Java heap space
Caused by: java.lang.OutOfMemoryError: Java heap space
at java.util.Arrays.copyOf(Arrays.java:2894)
at java.lang.AbstractStringBuilder.expandCapacity(AbstractStringBuilder.java:117)
at java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:407)
at java.lang.StringBuilder.append(StringBuilder.java:136)
ltimately you always have a finite max of heap to use no matter what platform you are running on. In Windows 32 bit this is around 2gb (not specifically heap but total amount of memory per process). It just happens that Java happens to make the default smaller (presumably so that the programmer can't create programs that have runaway memory allocation without running into this problem and having to examine exactly what they are doing).
So this given there are several approaches you could take to either determine what amount of memory you need or to reduce the amount of memory you are using. One common mistake with garbage collected languages such as Java or C# is to keep around references to objects that you no longer are using, or allocating many objects when you could reuse them instead. As long as objects have a reference to them they will continue to use heap space as the garbage collector will not delete them.
In this case you can use a Java memory profiler to determine what methods in your program are allocating large number of objects and then determine if there is a way to make sure they are no longer referenced, or to not allocate them in the first place. One option which I have used in the past is "JMP" http://www.khelekore.org/jmp/.
If you determine that you are allocating these objects for a reason and you need to keep around references (depending on what you are doing this might be the case), you will just need to increase the max heap size when you start the program. However, once you do the memory profiling and understand how your objects are getting allocated you should have a better idea about how much memory you need.
In general if you can't guarantee that your program will run in some finite amount of memory (perhaps depending on input size) you will always run into this problem. Only after exhausting all of this will you need to look into caching objects out to disk etc. At this point you should have a very good reason to say "I need Xgb of memory" for something and you can't work around it by improving your algorithms or memory allocation patterns. Generally this will only usually be the case for algorithms operating on large datasets (like a database or some scientific analysis program) and then techniques like caching and memory mapped IO become useful.
The OutOfMemoryError is usually caused by the VM not having enough memory to run your project. Did you run it directly from the command line or did you use an IDE ?
For example, Try running your programm with adding the -Xmx1G option which allocate 1Go of memory heap to your programm, you can of course adjust it to your convenience. the G is for Go and the m is for Mb.
You should give the heap a bigger size for it to work.
Related
I have troubles with Java memory consumption.
I'd like to say to Java something like this: "you have 8GB of memory, please use it, and only it. Only if you really can't put all your resources in this memory pool, then fail with OOM".
I know, there are default parameters like -Xmx - they limit only the heap. There are also plenty of other parameters, I know. The problems with these parameters are:
They aren't relevant. I don't want to limit the heap size to 6GB (and trust that native memory won't take more than 2GB). I do want to limit all the memory (heap, native, whatever). And do that effectively, not just saying "-Xmx1GB" - to be safe.
There is too many different parameters related to memory, and I don't know how to configure all of them to achieve the goal.
So, I don't want to go there and care about heap, perm and whatever types of memory. My high-level expectation is: since there is only 8GB, and some static memory is needed - take the static memory from the 8GB, and carefully split the remaining memory between other dynamic memory entities.
Also, ulimit and similar things don't work. I don't want to kill the java process once it consumes more memory than expected. I want Java does its best to not reach the limit firstly, and only if it really, really can't - kill the process.
And I'm OK to define even 100 java parameters, why not. :) But then I need assistance with the full list of needed parameters (for, say, Java 8).
Have you tried -XX:MetaspaceSize?
Is this what you need?
Please, read this article: http://karunsubramanian.com/websphere/one-important-change-in-memory-management-in-java-8/
Keep in mind that this is only valid to Java 8.
AFAIK, there is no java command line parameter or set of parameters that will do that.
Your best bet (IMO) is to set the max heap size and the max metaspace size and hope that other things are going to be pretty static / predictable for your application. (It won't cover the size of the JVM binary and it probably won't cover native libraries, memory mapped files, stacks and so on.)
In a comment you said:
So I'm forced to have a significant amount of memory unused to be safe.
I think you are worrying about the wrong thing here. Assuming that you are not constrained by address space or swap space limitations, memory that is never used doesn't matter.
If a page of your address space is not used, the OS will (in the long term) swap it out, and give the physical RAM page to something else.
Pages in the heap won't be in that situation in a typical Java application. (Address space pages will cycle between in-use and free as the GC moves objects within and between "spaces".)
However, the flip-side is that a GC needs the total heap size to be significantly larger than the sum of the live objects. If too much of the heap is occupied with reachable objects, the interval between garbage collection runs decreases, and your GC ergonomics suffer. In the worst case, a JVM can grind to a halt as the time spent in the GC tends to 100%. Ugly. The GC overhead limit mechanism prevents this, but that just means that your JVM gets an OOME sooner.
So, in the normal heap case, a better way to think about it is that you need to keep a portion of memory "unused" so that the GC can operate efficiently.
I am getting the following error on execution of a multi-threading program
java.lang.OutOfMemoryError: Java heap space
The above error occured in one of the threads.
Upto my knowledge, Heap space is occupied by instance variables only. If this is correct, then why this error occurred after running fine for sometime as space for instance variables are alloted at the time of object creation.
Is there any way to increase the heap space?
What changes should I made to my program so that It will grab less heap space?
If you want to increase your heap space, you can use java -Xms<initial heap size> -Xmx<maximum heap size> on the command line. By default, the values are based on the JRE version and system configuration. You can find out more about the VM options on the Java website.
However, I would recommend profiling your application to find out why your heap size is being eaten. NetBeans has a very good profiler included with it. I believe it uses the jvisualvm under the hood. With a profiler, you can try to find where many objects are being created, when objects get garbage collected, and more.
1.- Yes, but it pretty much refers to the whole memory used by your program.
2.- Yes see Java VM options
-Xms<size> set initial Java heap size
-Xmx<size> set maximum Java heap size
Ie
java -Xmx2g assign 2 gigabytes of ram as maximum to your app
But you should see if you don't have a memory leak first.
3.- It depends on the program. Try spot memory leaks. This question would be to hard to answer. Lately you can profile using JConsole to try to find out where your memory is going to
You may want to look at this site to learn more about memory in the JVM:
http://developer.streamezzo.com/content/learn/articles/optimization-heap-memory-usage
I have found it useful to use visualgc to watch how the different parts of the memory model is filling up, to determine what to change.
It is difficult to determine which part of memory was filled up, hence visualgc, as you may want to just change the part that is having a problem, rather than just say,
Fine! I will give 1G of RAM to the JVM.
Try to be more precise about what you are doing, in the long run you will probably find the program better for it.
To determine where the memory leak may be you can use unit tests for that, by testing what was the memory before the test, and after, and if there is too big a change then you may want to examine it, but, you need to do the check while your test is still running.
You can get your heap memory size through below programe.
public class GetHeapSize {
public static void main(String[] args) {
long heapsize = Runtime.getRuntime().totalMemory();
System.out.println("heapsize is :: " + heapsize);
}
}
then accordingly you can increase heap size also by using:
java -Xmx2g
http://www.oracle.com/technetwork/java/javase/tech/vmoptions-jsp-140102.html
To increase the heap size you can use the -Xmx argument when starting Java; e.g.
-Xmx256M
Upto my knowledge, Heap space is occupied by instance variables only. If this is correct, then why this error occurred after running fine for sometime as space for instance variables are alloted at the time of object creation.
That means you are creating more objects in your application over a period of time continuously. New objects will be stored in heap memory and that's the reason for growth in heap memory.
Heap not only contains instance variables. It will store all non-primitive data types ( Objects). These objects life time may be short (method block) or long (till the object is referenced in your application)
Is there any way to increase the heap space?
Yes. Have a look at this oracle article for more details.
There are two parameters for setting the heap size:
-Xms:, which sets the initial and minimum heap size
-Xmx:, which sets the maximum heap size
What changes should I made to my program so that It will grab less heap space?
It depends on your application.
Set the maximum heap memory as per your application requirement
Don't cause memory leaks in your application
If you find memory leaks in your application, find the root cause with help of profiling tools like MAT, Visual VM , jconsole etc. Once you find the root cause, fix the leaks.
Important notes from oracle article
Cause: The detail message Java heap space indicates object could not be allocated in the Java heap. This error does not necessarily imply a memory leak.
Possible reasons:
Improper configuration ( not allocating sufficiant memory)
Application is unintentionally holding references to objects and this prevents the objects from being garbage collected
Applications that make excessive use of finalizers. If a class has a finalize method, then objects of that type do not have their space reclaimed at garbage collection time. If the finalizer thread cannot keep up, with the finalization queue, then the Java heap could fill up and this type of OutOfMemoryError exception would be thrown.
On a different note, use better Garbage collection algorithms ( CMS or G1GC)
Have a look at this question for understanding G1GC
In most of the cases, the code is not optimized. Release those objects which you think shall not be needed further. Avoid creation of objects in your loop each time. Try to use caches. I don't know how your application is doing. But In programming, one rule of normal life applies as well
Prevention is better than cure. "Don't create unnecessary objects"
Local variables are located on the stack. Heap space is occupied by objects.
You can use the -Xmx option.
Basically heap space is used up everytime you allocate a new object with new and freed some time after the object is no longer referenced. So make sure that you don't keep references to objects that you no longer need.
No, I think you are thinking of stack space. Heap space is occupied by objects. The way to increase it is -Xmx256m, replacing the 256 with the amount you need on the command line.
To avoid that exception, if you are using JUnit and Spring try adding this in every test class:
#DirtiesContext(classMode = DirtiesContext.ClassMode.AFTER_CLASS)
I have tried all Solutions but nothing worked from above solutions
Solution: In My case I was using 4GB RAM and due to that RAM usage comes out 98% so the required amount if Memory wasn't available. Please do look for this also.If such issue comes upgrade RAM and it will work fine.
Hope this will save someone Time
In netbeans, Go to 'Run' toolbar, --> 'Set Project Configuration' --> 'Customise' --> 'run' of its popped up windo --> 'VM Option' --> fill in '-Xms2048m -Xmx2048m'. It could solve heap size problem.
I'm currently running my system against a rather large dataset and am getting the error. 'Out of memory. Java Heap Space'.
Is there anyway to get around this or is it just a case of the dataset is too large and can't be used?
In general, you can either
give it more memory e.g. increase the maximum heap size, but don't give it more than about 90% of main memory. BTW the default is 25% of main memory up to 32GB.
optimise the code so that it uses less memory, e.g. use a memory profiler. You can use a more efficient data structure or load portions of data into memory at a time.
break up the data so it own works on a portion at a time.
If it's not the dataset that's eating up memory, it could be that you are not freeing up objects once they are inactive.
This is typically due to keeping references to very large objects or to lots objects laying around long after they are no longer needed. This is most likely references that are static variables, but it can also be references to large temporary variables (e.g., largeStringBuilderobjects) within methods that are still active.
after searching the web for a while I decided to ask you for help with my problem.
My program should analyze logfiles, which are really big. They are about 100mb up to 2gb. I want to read the files using NIO-classes like FileChannel.
I don't want to save the files in memory, but I want to process the lines immediately. The code works.
Now my problem: I analyzed the Memory usage with the Eclipse MAT plugin and it says about 18mb of data is saved (that fits). But TaskManager in Windows says that about 180mb are used by the JVM.
Can you tell me WHY this is?
I don't want to save the data reading with the FileChannel, i just want to process it. I am closing the Channel afterwards - I thought every data would be deleted then?
I hope you guys can help me with the difference between the used space is shown in MAT and the used space is shown in TaskManager.
MAT will only show objects that are actively references by your program. The JVM uses more memory than that:
Its own code
Non-object data (classes, compiled bytecode e.t.c.)
Heap space that is not currently in use, but has already been allocated.
The last case is probably the most major one. Depending on how much physical memory there is on a computer, the JVM will set a default maximum size for its heap. To improve performance it will keep using up to that amount of memory with minimal garbage collection activity. That means that objects that are no longer referenced will remain in memory, rather than be garbage collected immediately, thus increasing the total amount of memory used.
As a result, the JVM will generally not free any memory it has allocated as part of its heap back to the system. This will show-up as an inordinate amount of used memory in the OS monitoring utilities.
Applications with high object allocation/de-allocation rates will be worse - I have an application that uses 1.8GB of memory, while actually requiring less than 100MB. Reducing the maximum heap size to 120 MB, though, increases the execution time by almost a full order of magnitude.
I have one probably dumb question. I am currently testing CSP solvers choco and jacop. When I run profiling of the app (graph colouring, about 3000 nodes), I dont fully understand the results.
The used heap space declared by profiler is about 1GB of memory. The sum of all object created is less than 100MB. Where are the other 900MB of RAM?
I think that method calls (solvers probably use massive backtracking) are being alocated on stack, so here should not be the problem. When I reduce maximum memory by using Xmx param, the app fails with exception:
Exception in thread "main" java.lang.OutOfMemoryError: GC overhead limit exceeded
So it seems, that the rest isnt unused uncollected memory (because in this case the GC would dealocate it (and would not fail)).
Thanks for your help.
Can you get a map of the heap? Most likely it's fragmented so those 100M of objects are spread out across the entire memory space. The memory needed is both a function of allocated objects and how fast they're being allocated and then de-referenced. That error means the memory area is too small for the work load, the garbage collector is consuming a lot CPU managing it, and it went beyond the allowed threshold.
Amir Afghani was probably correct in his comment. The classes (objects) in Netbeans 6.9.1 are probably somehow filtered (?or the profiler is bogus?), because when I performed the heap dump from java visual VM and analyzed it, it showed me !very! different numbers (which were in sum the same as the used heap).
Thanks for your replies.