CODEWITHSUNDEEP
java
user3809749
user3809749

Reputation: 129

Understanding java heap

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.

Upvotes: 7

Views: 8670

Answers (2)

f01
f01

Reputation: 1856

All the variables are documented here http://techupdates.com/go/884599

  • ErgoHeapSizeLimit that defaults to 0 means to ignore it. This limit is used if it is smaller than MaxRAM / MaxRAMFraction (fraction); zero means use MaxRAM / MaxRAMFraction [Source. Java Performance: The definitive guide (Scott Oaks, 2014)]

  • 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)

Upvotes: 0

Pier-Alexandre Bouchard
Pier-Alexandre Bouchard

Reputation: 5245

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)

Upvotes: 9

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