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In order to determine java heap size I used the following command:
java -XX:+PrintFlagsFinal -version -h | grep HeapSize
uintx ErgoHeapSizeLimit = 0 {product}
uintx HeapSizePerGCThread = 87241520 {product}
uintx InitialHeapSize := 1586475520 {product}
uintx LargePageHeapSizeThreshold = 134217728 {product}
uintx MaxHeapSize := 25383927808 {product}
java version "1.7.0_51"
Java(TM) SE Runtime Environment (build 1.7.0_51-b13)
Java HotSpot(TM) 64-Bit Server VM (build 24.51-b03, mixed mode)
However, I am unable to understand as to what is meant by ErgoHeapSizeLimit, HeapSizePerGCThread, InitialHeapSize, LargePageHeapSizeThreshold, MaxHeapSize, etc. Can someone please briefly explain these terms. Actually I am a complete novice at java
Actually I need to determine the heap size which my machine can allocate to a process? Because one of my application demands the following parameters: -server, -Xmx16G or better, etc. to be set.
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The Java heap is the area of memory used to store objects instantiated by applications running on the JVM. When the JVM is started, heap memory is created and any objects in the heap can be shared between threads as long as the application is running.
Heap space is used for the dynamic memory allocation of Java objects and JRE classes at runtime. New objects are always created in heap space, and the references to these objects are stored in stack memory. These objects have global access and we can access them from anywhere in the application.
The Java™ virtual machine (JVM) heap is an independent memory allocation that can reduce the capacity of the main memory heap. Every integration server creates its own JVM. The integration server uses the JVM to execute the internal administration threads that require Java. This usage is typically minimal.
It is recommended to increase the Java heap space only up to one-half of the total RAM available on the server. Increasing the Java heap space beyond that value can cause performance problems. For example, if your server has 16 GB of RAM available, then the maximum heap space you should use is 8 GB.
Take a look here (they were extracted from OpenJDK):
http://jvm-options.tech.xebia.fr/
ErgoHeapSizeLimit: Maximum ergonomically set heap size (in bytes); zero means use MaxRAM / MaxRAMFraction
HeapSizePerGCThread: Size of heap (bytes) per GC thread used in calculating the number of GC threads
InitialHeapSize: Initial heap size (in bytes); zero means OldSize + NewSize
LargePageHeapSizeThreshold: Use large pages if max heap is at least this big
MaxHeapSize: Maximum heap size (in bytes)
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