A short talk about metaspaces.

1. ilJUG
Java
8
Launch
Event
#2
Metaspaces
!
Haim Yadid - Performize-IT

2. About
Me:
Haim
Yadid
•21 Years of SW development experience
•Performance Expert
•Consulting R&D Groups
•Training: Java Performance Optimization
•Organizing : ILJUG

3. IL
JUG
•Israeli Java User Group
•Reborn at 1/14
•Meetup : http://www.meetup.com/IL-JUG
•G+: https://plus.google.com/u/0/communities/110138558454900054301
•Twitter: @il_jug

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Major Memory Regions
Monitoring the JVM
Young PermTenured
Code
Cache
Heap
Permanent generation
Code Cache
Native Memory
Heap Non Heap
NativeNative

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Monitoring Memory
Jconsole Memory tab
Jconsole overview tab
Mbeans java.lang/Memory
HeapMemoryUsage
Operation : gc
Mbeans java.lang/MemoryPool
Per memory pool usage
Jstat –gccapacity
Monitoring the JVM

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Permanent Generation
Holds class metadata
Holds interned strings
Classes may get collected (unloaded) if JVM finds
they are no longer needed
Monitoring the JVM

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Interning Strings
Strings are immutable
If two strings are equal a same string object can be
used.
Automatic for constant strings
Requires intervention in some cases
String a = “Hello world”
String b = “Hello world”
String c = a+b;
String d = a+b;
c!= d!!!!
Tuning Memory: Memory Areas

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Interning Strings (Cont)
String.intern() always will return the same object
Use it when
The domain is relatively small
Trade memory for speed interning strings takes time
Stored in the PERMGEN
Requires larger PERMGEN size
Tuning Memory: Memory Areas

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Out of memory Heap space
Exception in thread "main" java.lang.OutOfMemoryError:
Java heap space
Solutions:
Increase heap memory
Analyze stack trace where OOM occurred
Analyze memory dump (next chapter)
Tuning Memory: OOM

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Permanent Generation
When memory is not an issue set
-XX:MaxPermSize=<n>
-XX:PermSize=<n>
Enable PermGen GC on CMS
-XX:+CMSClassUnloadingEnabled
-XX:+PermGenSweepingEnabled (not required for
HotSpot Java 6 JVMs.).
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Tuning Memory: Memory Areas

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Tuning Permanent Generation
Usually needed !
Required when:
Application codebase is large
String intern is extensively used
Find smallest permgen that will not throw OOM
errors.
Cover all areas of the application
Leave additional 10MB free
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Tuning Memory: Memory Areas

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Meta spaces - In J8
Permanent generation is removed
Part of the native memory
Not continuous with the Heap (good for 32 bit JVMs)
Better for GC performance
special process for metaspace
Deallocate class concurrently and not in GC pause
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Tuning Memory: Memory Areas

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Allocation in Metaspace
Multiple memory map / virtual alloc
Allocate address space per class loader
Virtual address space return when class loader
released
minimize fregmentation
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Tuning Memory: Memory Areas

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Configuration
-XX:MaxMetaspaceSize={unlimited}
By default
Limited by memory + swap space
Address space 32 bit
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Tuning Memory: Memory Areas

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More configuration
InitialBootClassLoaderMetaspaceSize 4194304
MaxMetaspaceExpansion 5451776
MaxMetaspaceFreeRatio 70
MaxMetaspaceSize 18446744073709547520
MetaspaceSize 21807104
MinMetaspaceExpansion 339968
MinMetaspaceFreeRatio 40
UseLargePagesInMetaspace
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Tuning Memory: Memory Areas

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Monitoring
jmap -clstats <pid>
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Tuning Memory: Memory Areas

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Monitoring
jstat -gc <pid>
!
!
S0C S1C S0U S1U EC EU OC OU MC MU CCSC CCSU ….
3584.0 3584.0 0.0 224.0 87040.0 45719.4 29184.0 21994.1 32768.0 31755.8 3840.0 3582.8 …
© Copyright Performize IT LTD.
Tuning Memory: Memory Areas

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Monitoring
jstat -gc <pid>
!
!
S0C S1C S0U S1U EC EU OC OU MC MU CCSC CCSU ….
3584.0 3584.0 0.0 224.0 87040.0 45719.4 29184.0 21994.1 32768.0 31755.8 3840.0 3582.8 …
© Copyright Performize IT LTD.
Tuning Memory: Memory Areas

20. Thanks + Q&A + Contact Me
© Copyright Performize-IT LTD.
http://il.linkedin.com/in/haimyadid
lifey@performize-it.com
www.performize-it.com
blog.performize-it.com
https://github.com/lifey
@lifeyx