Heap space out of memory

Question

My application currently consumes quite a lot of memory because it is running physics simulations  The issue is that consistently  at the 51st simulation  Java will throw an error usually because of a heap space out of memory  my program eventually runs thousands of simulations   Is there anyway I can not just increase the heap space but modify my program so that the heap space is cleared after every run so that I can run an arbitrary number of simulations  Edit  Thanks guys  Turns out the simulator software wasn t clearing the information after every run and I had those runs all stored in an ArrayList

User · Answer

There is no way to dynamically increase the heap programatically since the heap is allocated when the Java Virtual Machine is started.

However, you can use this command

java -Xmx1024M YourClass

to set the memory to 1024

or, you can set a min max

java -Xms256m -Xmx1024m YourClassNameHere

User · Answer

There are a variety of tools that you can use to help diagnose this problem  The JDK includes JVisualVM that will allow you to attach to your running process and show what objects might be growing out of control  Netbeans has a wrapper around it that works fairly well  Eclipse has the Eclipse Memory Analyzer which is the one I use most often  just seems to handle large dump files a bit better  There s also a command line option  -XX  HeapDumpOnOutOfMemoryError that will give you a file that is basically a snapshot of your process memory when your program crashed  You can use any of the above mentioned tools to look at it  it can really help a lot when diagnosing these sort of problems   Depending on how hard the program is working  it may be a simple case of the JVM not knowing when a good time to garbage collect may be  you might also look into the parallel garbage collection options as well

User · Answer

Try adding -Xmx for more memory   java -Xmx1024M YourClass    and don t forget to stop referencing variables you don t need any more  memory leaks

User · Answer

If you are using a lot of memory and facing memory leaks  then you might want to check if you are using a large number of ArrayLists or HashMaps with many elements each   An ArrayList is implemented as a dynamic array  The source code from Sun Oracle shows that when a new element is inserted into a full ArrayList  a new array of 1 5 times the size of the original array is created  and the elements copied over  What this means is that you could be wasting up to 50  of the space in each ArrayList you use  unless you call its trimToSize method  Or better still  if you know the number of elements you are going to insert before hand  then call the constructor with the initial capacity as its argument   I did not examine the source code for HashMap very carefully  but at a first glance it appears that the array length in each HashMap must be a power of two  making it another implementation of a dynamic array  Note that HashSet is essentially a wrapper around HashMap

User · Answer

Are you keeping references to variables that you no longer need  e g  data from the previous simulations   If so  you have a memory leak  You just need to find where that is happening and make sure that you remove the references to the variables when they are no longer needed  this would automatically happen if they go out of scope    If you actually need all that data from previous simulations in memory  you need to increase the heap size or change your algorithm

User · Answer

I would like to add that this problem is similar to common Java memory leaks   When the JVM garbage collector is unable to clear the  waste  memory of your Java   Java EE application over time  OutOfMemoryError  Java heap space will be the outcome   It is important to perform a proper diagnostic first    Enable verbose gc  This will allow you to understand the memory growing pattern over time  Generate and analyze a JVM Heap Dump  This will allow you to understand your application memory footprint and pinpoint the source of the memory leak s   You can also use Java profilers and runtime memory leak analyzer such as Plumbr as well to help you with this task

User · Answer

No  The heap is cleared by the garbage collector whenever it feels like it  You can ask it to run  with System gc    but it is not guaranteed to run   First try increasing the memory by setting -Xmx256m

User · Answer

I also faced the same problem I resolved by doing the build by following steps as   -- Right click on the project select RunAs - Run configurations  Select your project as BaseDirectory  In place of goals give eclipse eclipse install  -- In the second tab give -Xmx1024m as VM arguments

User · Answer

Java is supposed to clear the heap space for you when all of the objects are no longer referenced   It won t generally release it back to the OS though  it will keep that memory for it s own internal reuse   Maybe check to see if you have some arrays which are not being cleared or something

[java] Heap space out of memory

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