JVM GC算法简介

1. JVM GC
by

2. Outline
JVM 结 简
Hotspot JVM GC 绍
JVM GC
Levit JVM

3. JVM Structure
class files class loader
Runtime Data Area
Native
Method Area Java Stack Method
Stack
Heap PC Register
Execute Native Native
Engine Interface Library

4. Heap
Java new 对
Method Area
Java Stack Java栈&Native Statck
栈

5. HotSpot JVM GC
weak generational hypothesis:
Most allocated objects are not
referenced (considered live) for long,
that is, they die young.
Few references from older to younger
objects exist.

6. Heap
Young Generation
Eden
From To
Old Generation
Tenured Space

7. -Xmxn 间
-Xmsn 间
-Xmnn young
-XX:PermSize=n 间

8. GC
Minor GC
young generation满 时
minor collection
Full GC
old permanent满 时 进 full

9. GC
VS
发VS Stop-the-World
压缩 VS 压缩 VS 贝

10. GC
Eden
From To
Empty
Old

11. GC
Eden
Empty
To From
Empty
Old

12. Old GC
mark
sweep
compact

13. GC
Client 认
-XX:+UseSerialGC

14. GC
young Parallel Scavenage GC
old Parallel MSC GC

15. Parallel Scavenge GC

16. Parallel Scavenge GC
Eden
From To

17. Parallel Scavenge GC
Eden
From To

18. Parallel Scavenge GC
Eden
From To

19. Parallel MSC GC

20. Parallel MSC GC
R1: R2:4/6 R3:3/6 R4:1/6 R5:0/6

21. Parallel MSC GC
destination region source region
R1: R2:4/6 R3:3/6 R4:1/6 R5:0/6
Dense prefix

22. Parallel MSC GC
R1: R2:4/6 R3:3/6 R4:1/6 R5:0/6
T2 T1

23. Parallel MSC GC
R1 R2 R3 R4 R5
T2 T1

24. Parallel MSC GC
R1 R2 R3 R4 R5
T2 T1

25. GC
Server 认
-XX:+UseParallelGC

26. CMS GC

27. CMS GC

28. CMS 动 产

29. CMS
-XX:+UseConcMarkSweepGC

30. GC
F ir st
r ba ge
Ga
http://research.sun.com/jtech/pubs/04-g1-paper-ismm.pdf

31. GC组

32. JVM
http://blogs.oracle.com/watt/resource/jvm-options-list.html

33. JVM GC
jstat
jmap
jconsole
jvisualvm

34. Levit JVM
-Xmx2g 2G
-Xms2g 2G
-Xmn512m young 512M
-XX:PermSize=128m Perm 128M
-XX:MaxPermSize=196m Perm 196M
-Xss256k 256K

35. Levit JVM
-XX:+DisableExplicitGC GC System.gc() JVM
GC
-XX:+UseConcMarkSweepGC CMS GC
-XX:+CMSParallelRemarkEnabled CMS remark remark
-XX:+UseParNewGC
-XX:+UseCMSCompactAtFullCollection:CMS Compact
-XX:+UseFastAccessorMethods:Use optimized versions of
Get<Primitive>Field.
-XX:+UseCMSInitiatingOccupancyOnly :Used to enabled/disable the use of the
anticipated promotions to start a concurrent collection set
-XX:+UseCompressedOops : 64 64
32Gb 32

38. GC

39. FullGC 应 频 启
压 长 YoungGC

40. 资
http://chaoticjava.com/posts/parallel-and-concurrent-garbage-collectors
http://blogs.oracle.com/watt/resource/jvm-options-list.html
http://www.oracle.com/technet work/java/javase/tech/index-
jsp-136373.html

41. Any Questi ons
Q&A