What is left is the other user land processes that may be running on the host and the other types of memory that the JVM needs (eg for stack). Again, remember that this is 75% of the RAM available, not the RAM installed. If you are on Linux, only running standard daemons and have installed RAM from somewhere around 1 Gb and up then I wouldn't hesitate to use 75% for the JVM's heap. My own rule: If your host is more or less dedicated to running the given java application, then you can without problems increase dramatically. The default value for MaxRAMPercentage is 25%. Note that the options are mentioned under a Docker heading but in fact they apply whether you are in Docker environment or in a traditional environment. See Release Notes for Java8 u191 for more information. (which is same as the RAM installed less what the kernel uses). That can be used to size the heap as a percentage of the usable physical RAM. From Ergonomics in the 5.0 JavaTM Virtual Machine:Īs of Java 8u191 you now have the options: -XX:InitialRAMPercentage Before J2SE 5.0, theĪs pointed out by Tom Anderson in his comment, the above is for server-class machines. Smaller of 1/4th of the physical memory or 1GB. Larger of 1/64th of the machine's physical memory on the machine or some For most JVM implementations, the most important of those options are -Xmx and -Xms.For Java SE 5: According to Garbage Collector Ergonomics : Command line options for the JVM can control how much memory is made available. If you do not explicitly tell the JVM how much memory to use, most implementations will choose a sensible default amount based on the amount of RAM that your computer has, but that amount could be too small for your program. You might conclude that you program is behaving correctly, but just needs more memory to run than has been made available to it. The JVM has a finite amount of memory made available to it. It can provide information about the sizes, number and classes of objects stored in memory. That is a monitoring program that enables you to examine the memory used for objects while the program runs, or examies a heap dump written when the program exits. If the stacktrace does not provide enough clues, you could try using a heap profiler. Is your loop termination condition correct? If it is a for loop, are you asking it to loop the correct number of times? If the exception is thrown from inside a loop, the cause could be that the code has looped too many times.Have you made a mistake in the calculation of the size of container you need? Methods such as ArrayList.reserve(int) and HashMap(int) must allocate storage for future use. If the exception is thrown from an attempt to allocate an array in a method of a container class written by someone else, the cause could be that your code is asking the container to store an excessive number of things.Have you made a mistake in the calculation of the size of array you need? If the exception is thrown from an attempt to allocate an array (such as int values = new int), the cause could be that you are trying to create an excessively large array ( n is too large). Therefore, you should first examine the stacktrace associated with the exception for clues about the cause of the problem, as you would for any other exception. However, in practice it is likely to be thrown from a new statement that tried to create an object for which memory could not be allocated. The JVM will have first tried to free memory used by dead objects, by running the garbage collector.Īs an OutOfMemoryError is a VirtualMachineError, the JVM is permitted to throw it at any time, although it must try to release memory through garbage collection first. An OutOfMemoryError is an exception thrown by the Java Virtual Machine (JVM) because it needs to allocate memory for a (new) object, but insufficient memory is available for the object.
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