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Can't allocate more than 183MB on IBM Java VM  XML
Forum Index -> BigMemory
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[Post New]09/25/2012 07:05:51
    Subject: Can't allocate more than 183MB on IBM Java VM
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kborgul

neo

Joined: 09/25/2012 06:59:55
Messages: 2
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I run my sample program using Bigmemory with parameter: -XX:MaxDirectMemorySize=512m, but I can't create OffHeapStore greater than 183 MB (otherwise I am receiving OOME). I am using IBM Java VM.

>java -version
java version "1.6.0"
Java(TM) SE Runtime Environment (build pwi3260_26sr1-20111114_01(SR1))
IBM J9 VM (build 2.6, JRE 1.6.0 Windows XP x86-32 20111113_94967 (JIT enabled, A
OT enabled)
J9VM - R26_Java626_SR1_20111113_1649_B94967
JIT - r11_20111028_21230
GC - R26_Java626_SR1_20111113_1649_B94967
J9CL - 20111113_94967)
JCL - 20111112_01
[Post New]09/25/2012 07:29:46
    Subject: Re:Can't allocate more than 183MB on IBM Java VM
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klalithr

consul

Joined: 01/23/2011 10:58:07
Messages: 489
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Can you explain what you are trying to do. Are you using the new BigMemory Go project. Are you using the Server Array. Why are you only allocating 512MB of space - Why not use the heap instead ?
Karthik Lalithraj (Terracotta)
[Post New]09/25/2012 11:55:11
    Subject: Re:Can't allocate more than 183MB on IBM Java VM
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lorban

jedi

Joined: 01/08/2010 13:09:16
Messages: 101
Location: CET
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According to the version info you posted, it looks like you're using a 32-bit JVM.

This would definitely explain why you can only allocate very little offheap as the virtual address space is limited to only 4GB. Check this link to know more about the limitations of Big Memory with 32-bit JVMs: http://ehcache.org/documentation/user-guide/bigmemory#using-offheapstore-with-32-bit-jvms

I'm highly recommending you to use a 64-bit JVM for Big Memory or you're going to be so constrained that it won't help much.
Ludovic Orban (Terracotta engineer)
[Post New]09/26/2012 00:00:15
    Subject: Re:Can't allocate more than 183MB on IBM Java VM
[Up]
kborgul

neo

Joined: 09/25/2012 06:59:55
Messages: 2
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Yes, I think it is related to 32-bit VM and different behavior of IBM VM.
Oracle 32-bit VM has no problem with creating eg. 500MB offheap cache with MaxDirectMemorySize=1024m
[Post New]09/26/2012 08:30:09
    Subject: Re:Can't allocate more than 183MB on IBM Java VM
[Up]
lijie

journeyman

Joined: 09/04/2012 23:10:13
Messages: 19
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And check this link for Allocating Direct Memory in the JVM: http://ehcache.org/documentation/configuration/bigmemory#configuration

NOTE: Direct Memory and Off-heap Memory Allocations

To accommodate server communications layer requirements, the value of maxDirectMemorySize must be greater than the value of maxBytesLocalOffHeap. The exact amount greater depends upon the size of maxBytesLocalOffHeap. The minimum is 256MB, but if you allocate 1GB more to the maxDirectMemorySize, it will certainly be sufficient. The server will only use what it needs and the rest will remain available.
 

 
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