The JVM - Internal ( 스터디 자료 )

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The JVM

2015.06 Gun Lee

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JVM에 대해 스터디하던 내용을

정리하여 공유합니다.

많은 부분이 엑셈에서 출판된

Java Performance Fundmental(김한도 저)

에서 발췌하였습니다.

제 슬라이드는 단지 이에 대한 소개이므로

더 깊은 내용은 위 도서를 직접 보시는 것을 강추!! 드립니다. ^^

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What is the JVM?

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What is the JVM?

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… is Java virtual Machine…

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What is the JVM?

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Write Once, run everywhere

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What is the JVM?

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JVM Architecture

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Class, Classloader

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Class, Classloader

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bytecode

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Class, Classloader

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source

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Class, Classloader

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javap –c

bytecode

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Class, Classloader

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javap –verbose

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Class, Classloader

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Constant pool

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Class, Classloader

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opcode, operand

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Class, Classloader

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classloader

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Class, Classloader

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Namespace

- classloader 마다 존재

- class의 구분 namespace + full qualified name

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Class, Classloader

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Namespace

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Class, Classloader

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delegation model

class visibility

Parent first

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Class, Classloader

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ClassNotFoundException

!

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Class, Classloader

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Classloader Tree in WAS

Isolating the Application from other Applications

Sharing Class between deployed module

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Class, Classloader

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Classloader Tree in WAS

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Class, Classloader

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parent-first, child-last?

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Class, Classloader

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parent-first, child-last?

Not always

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Class, Classloader

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parent-first, child-last?

- Tomcat Bootstrap System WEB-INF/classes/* WEB-INF/lib/* Common Vendor specific extensions!

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Class, Classloader

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Class

Classloader

constant pool bytecode local variable table

namespace delegation model - parent first

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Execution Engine

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Execution Engine

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execute bytecodes

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Execution Engine

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Interpreter

JIT(Just In Time) Compiler

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Execution Engine

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Interpreter

read the bytecode line by line

no optimization

parsing & executing

해석시간은 짧으나 실행시간은 길다!

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Execution Engine

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JIT Compiler

loads the whole method

generates native code

optimization

Native로 컴파일 하는 시간이 긺

여러 번 호출시 이득

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Execution Engine

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JIT Compiler

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Execution Engine

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Hotspot Compiler

Mixed mode system

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Execution Engine

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Hotspot Compiler

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Execution Engine

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Server VM vs Client VM

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Execution Engine

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Server VM vs Client VM

Server VM – advanced adaptive compiler runtime performance profiling, optimizing

Client VM - better for GUI run faster smaller memory footprint

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Execution Engine

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Profiling & Optimization

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Execution Engine

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Profiling & Optimization

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Execution Engine

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Profiling & Optimization

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Execution Engine

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JVM Options

-Xint

-XX:CompileThreshold=<value> Client:1,500, Server:10,000

-Xcomp

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Runtime Data Area

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Runtime Data Area

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Runtime Data Area

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Runtime Data Area

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Runtime Data Area

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Runtime Data Area

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Method area and Heap shared among all threads

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Runtime Data Area

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Method area

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Runtime Data Area

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Method area Type Information (Runtime) Constant Pool field Information Method Information

(& bytecode) Class Variables …

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Runtime Data Area

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Method area Type Information (Runtime) Constant Pool field Information Method Information

(& bytecode) Class Variables …

Class??

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Runtime Data Area

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Heap

a = new myObj();

b = new myObj();

Heap

Method Area Class

obj

obj

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Runtime Data Area

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Heap

Check it out later…

The chapter. Garbage Collection

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Runtime Data Area

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exclusive to each thread

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Runtime Data Area

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PC register(Program counter)

contains the address of the Java Virtual Machine instruction currently being executed

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Runtime Data Area

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JVM Stacks

Stack Trace

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Runtime Data Area

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stack trace

stackframe

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Runtime Data Area

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JVM Stacks http://www.slideshare.net/novathinker/2-runtime-

data-areas

- Page 68.

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Runtime Data Area

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Runtime Data Area

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Garbage Collector

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Garbage Collector

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GC ????

Stop the World !!

Out of Memory !!

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Garbage Collector

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GC of Hotspot JVM

Weak Generation Hypothesis - High Infant Mortality

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Garbage Collector

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Heap of Hotspot JVM

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Garbage Collector

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GC & Reachability

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Garbage Collector

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GC & Reachability

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Garbage Collector

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Bump the pointer & TLAB (Thread Local Allocation Barrier)

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Garbage Collector

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Mark alive object

--> Reachable from Rootset.

reference from Old Gen???

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Garbage Collector

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Card Table & Write Barrier

1 byte card per 512 byte Old gen.

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Garbage Collector

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Card Table & Write Barrier

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Garbage Collector

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Minor GC - young Gen. Mark & Copy

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Garbage Collector

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Full GC - Old Gen. Mark & sweep & compaction

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Garbage Collector

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Parallel Collector – young gen.

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Garbage Collector

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Parallel Collector – young gen.

Options

-XX:+UseParallelGC

-XX:ParallelGCThreds=<value>

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Garbage Collector

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Parallel Compacting Collector - old Gen.

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Garbage Collector

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Parallel Compacting Collector

Options

-XX:+UseParallelOldGC (+Java6)

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Garbage Collector

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Parallel Compacting Collector

Options

-XX:+UseParallelOldGC (+Java6)

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Garbage Collector

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CMS Collector – Old Gen

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Garbage Collector

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CMS Collector – Old Gen

short pausing time No Compaction

-> disadvantage for fast allocation in promotion.

if the compaction task is needed, the STW time can be longer than any

other GC types.

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Garbage Collector

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CMS Collector – Old Gen

Options

-XX:+UseConcMarkSweepGC

-XX:+UseParNewGC

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Garbage Collector

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GC log Options

-XX:+DisableExplicitGC

-XX:+PrintGCDetails

-XX:+PrintGCTimeStamps

-Xloggc

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Garbage Collector

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IBM JVM

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Garbage Collector

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Pinned Class problem

[AF] Allocation Failure action=0

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Garbage Collector

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IBM JVM – GC Options

-Xgcpolicy:<options> optthruput optavgpause gencon subpool

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Garbage Collector

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Visual GC animation http://haks1999.github.io/haklab-gc/serial.html

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Garbage Collector

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Heap memory tuning test

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Garbage Collector

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verbose GC analysis

HPJmeter, IBM GC Analyzer…

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and more…

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Trouble shootings

Thread Dump Analysis Heap Dump Analysis

GC Log Analysis

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References ( contents, images )

http://www.oracle.com/technetwork/java/whitepaper-135217.html http://www.oracle.com/technetwork/java/javase/memorymanagement-whitepaper-150215.pdf http://www.artima.com/insidejvm/ed2/jvm.html http://javapapers.com/core-java/java-jvm-run-time-data-areas/ http://blog.ragozin.info/2011/06/understanding-gc-pauses-in-jvm-hotspots.html http://tomcat.apache.org/tomcat-8.0-doc/class-loader-howto.html http://epicdevs.com/16 http://blog.naver.com/bumsukoh/110113098160 http://helloworld.naver.com/helloworld/1230 http://helloworld.naver.com/helloworld/1329 http://helloworld.naver.com/helloworld/329631 http://www.slideshare.net/novathinker/1-java-key http://www.slideshare.net/novathinker/2-runtime-data-areas http://www.slideshare.net/novathinker/3-garbage-collection http://www.slideshare.net/novathinker/4-class-loader http://www.slideshare.net/novathinker/5-execution-engine https://www.ibm.com/developerworks/community/blogs/738b7897-cd38-4f24-9f05-48dd69116837/entry/troubleshooting_and_memory_leak_analysis_with_java_data_objects_framework18?lang=en Java Performance(by Charlie Hunt , Binu John) / Addison-Wesley JAVA PERFORMANCE FUNDAMENTAL(김한도 저) / 엑셈

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Thank you !

Q&A or later

gunlee01@gmail.com

http://facebook.com/gunlee01