JVM에 대한 스터디 자료입니다. Classloader, Execution Engine, Runtime data area, garbage collector 등 JVM 내부를 다룹니다.

1. /83
The JVM
2015.06
Gun Lee
1

2. /832
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. ^^

3. /83
What is the JVM?
3

4. /83
What is the JVM?
4
… is
Java virtual Machine…

5. /83
What is the JVM?
5
Write Once, run everywhere

6. /83
What is the JVM?
6
JVM Architecture

7. /83
Class, Classloader
7

8. /83
Class, Classloader
8
bytecode

9. /83
Class, Classloader
9
source

10. /83
Class, Classloader
10
javap –c
bytecode

11. /83
Class, Classloader
11
javap –verbose

12. /83
Class, Classloader
12
Constant pool

13. /83
Class, Classloader
13
opcode, operand

14. /83
Class, Classloader
14
classloader

15. /83
Class, Classloader
15
Namespace
- classloader 마다 존재
- class의 구분
namespace + full qualified name

16. /83
Class, Classloader
16
Namespace

17. /83
Class, Classloader
17
delegation model
class visibility
Parent first

18. /83
Class, Classloader
18
ClassNotFoundException
!

19. /83
Class, Classloader
19
Classloader Tree in WAS
Isolating the Application from other
Applications
Sharing Class between deployed module

20. /83
Class, Classloader
20
Classloader Tree in WAS

21. /83
Class, Classloader
21
parent-first, child-last?

22. /83
Class, Classloader
22
parent-first, child-last?
Not always

23. /83
Class, Classloader
23
parent-first, child-last?
- Tomcat
Bootstrap
System
WEB-INF/classes/*
WEB-INF/lib/*
Common
Vendor specific extensions!

24. /83
Class, Classloader
24
Class
Classloader
constant pool
bytecode
local variable table
namespace
delegation model
- parent first

25. /83
Execution Engine
25

26. /83
Execution Engine
26
execute bytecodes

27. /83
Execution Engine
27
Interpreter
JIT(Just In Time) Compiler

28. /83
Execution Engine
28
Interpreter
read the bytecode line by line
no optimization
parsing & executing
해석시간은 짧으나 실행시간은 길다!

29. /83
Execution Engine
29
JIT Compiler
loads the whole method
generates native code
optimization
Native로 컴파일 하는 시간이 긺
여러 번 호출시 이득

30. /83
Execution Engine
30
JIT Compiler

31. /83
Execution Engine
31
Hotspot Compiler
Mixed mode system

32. /83
Execution Engine
32
Hotspot Compiler

33. /83
Execution Engine
33
Server VM vs Client VM

34. /83
Execution Engine
34
Server VM vs Client VM
Server VM – advanced adaptive compiler
runtime performance
profiling, optimizing
Client VM - better for GUI
run faster
smaller memory footprint

35. /83
Execution Engine
35
Profiling & Optimization

36. /83
Execution Engine
36
Profiling & Optimization

37. /83
Execution Engine
37
Profiling & Optimization

38. /83
Execution Engine
38
JVM Options
-Xint
-XX:CompileThreshold=<value>
Client:1,500, Server:10,000
-Xcomp

39. /83
Runtime Data Area
39

40. /83
Runtime Data Area
40
Runtime Data Area

41. /83
Runtime Data Area
41
Runtime Data Area

42. /83
Runtime Data Area
42
Method area and Heap
shared among all threads

43. /83
Runtime Data Area
43
Method area

44. /83
Runtime Data Area
44
Method area
Type Information
(Runtime) Constant Pool
field Information
Method Information
(& bytecode)
Class Variables
…

45. /83
Runtime Data Area
45
Method area
Type Information
(Runtime) Constant Pool
field Information
Method Information
(& bytecode)
Class Variables
…
Class??

46. /83
Runtime Data Area
46
Heap
a = new myObj();
b = new myObj();
Heap
Method
Area
Class
obj
obj

47. /83
Runtime Data Area
47
Heap
Check it out later…
The chapter. Garbage Collection

48. /83
Runtime Data Area
48
exclusive to each thread

49. /83
Runtime Data Area
49
PC register(Program counter)
contains the address of the Java Virtual
Machine instruction currently being
executed

50. /83
Runtime Data Area
50
JVM Stacks
Stack Trace

51. /83
Runtime Data Area
51
stack trace
stackframe

52. /83
Runtime Data Area
52
JVM Stacks
http://www.slideshare.net/novathinker/2-runtime-
data-areas
- Page 68.

53. /83
Runtime Data Area
53
Runtime Data Area

54. /83
Garbage Collector
54

55. /83
Garbage Collector
55
GC ????
Stop the World !!
Out of Memory !!

56. /83
Garbage Collector
56
GC of Hotspot JVM
Weak Generation Hypothesis
- High Infant Mortality

57. /83
Garbage Collector
57
Heap of Hotspot JVM

58. /83
Garbage Collector
58
GC & Reachability

59. /83
Garbage Collector
59
GC & Reachability

60. /83
Garbage Collector
60
Bump the pointer & TLAB
(Thread Local Allocation Barrier)

61. /83
Garbage Collector
61
Mark alive object
--> Reachable from Rootset.
reference from Old Gen???

62. /83
Garbage Collector
62
Card Table & Write Barrier
1 byte card per 512 byte Old gen.

63. /83
Garbage Collector
63
Card Table & Write Barrier

64. /83
Garbage Collector
64
Minor GC - young Gen.
Mark & Copy

65. /83
Garbage Collector
65
Full GC - Old Gen.
Mark & sweep & compaction

66. /83
Garbage Collector
66
Parallel Collector – young gen.

67. /83
Garbage Collector
67
Parallel Collector – young gen.
Options
-XX:+UseParallelGC
-XX:ParallelGCThreds=<value>

68. /83
Garbage Collector
68
Parallel Compacting Collector
- old Gen.

69. /83
Garbage Collector
69
Parallel Compacting Collector
Options
-XX:+UseParallelOldGC (+Java6)

70. /83
Garbage Collector
70
Parallel Compacting Collector
Options
-XX:+UseParallelOldGC (+Java6)

71. /83
Garbage Collector
71
CMS Collector – Old Gen

72. /83
Garbage Collector
72
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.

73. /83
Garbage Collector
73
CMS Collector – Old Gen
Options
-XX:+UseConcMarkSweepGC
-XX:+UseParNewGC

74. /83
Garbage Collector
74
GC log Options
-XX:+DisableExplicitGC
-XX:+PrintGCDetails
-XX:+PrintGCTimeStamps
-Xloggc

75. /83
Garbage Collector
75
IBM JVM

76. /83
Garbage Collector
76
Pinned Class problem
[AF]
Allocation Failure
action=0

77. /83
Garbage Collector
77
IBM JVM – GC Options
-Xgcpolicy:<options>
optthruput
optavgpause
gencon
subpool

78. /83
Garbage Collector
78
Visual GC animation
http://haks1999.github.io/haklab-gc/serial.html

79. /83
Garbage Collector
79
Heap memory tuning test

80. /83
Garbage Collector
80
verbose GC analysis
HPJmeter, IBM GC Analyzer…

81. /83
and more…
81
Trouble shootings
Thread Dump Analysis
Heap Dump Analysis
GC Log Analysis

82. /83
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
82

83. /8383
Thank you !
Q&A or later
gunlee01@gmail.com
http://facebook.com/gunlee01