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![Performance
Impact
of
GC
5
Java
SE
6
HotSpot[tm]
Virtual
Machine
Garbage
CollecRon
Tuning
h[p://www.oracle.com/technetwork/java/javase/gc-‐tuning-‐6-‐140523.html
0.6
0.2
8
32](https://image.slidesharecdn.com/javagcjavadeveloperdaytw-140801231304-phpapp02/85/Java-GC-5-320.jpg)
![• Java
Performance
–
Charlie
Hunt,
Binu
John
• HotSpot
GC
Tuning
Guide
for
Java
SE
6
h[p://www.oracle.com/technetwork/java/javase/gc-‐
tuning-‐6-‐140523.html
• Memory
Management
in
the
Java
HotSpot
VM
h[p://www.oracle.com/technetwork/java/javase/
memorymanagement-‐whitepaper-‐150215.pdf
• Java
6
Performance
Whitepaper
h]p://java.sun.com/performance/reference/whitepapers/6_performance.html
78](https://image.slidesharecdn.com/javagcjavadeveloperdaytw-140801231304-phpapp02/85/Java-GC-78-320.jpg)
Uploaded byLeon Chen
淺談 Java GC 原理、調教和 新發展
This document provides an overview of garbage collection in Java. It begins with an introduction to the presenter Leon Chen and his background. It then discusses Java memory management and garbage collection fundamentals, including the young and old generations, minor and major garbage collections, and how objects are promoted between generations. The document provides examples of garbage collection using diagrams and discusses tuning the Java heap size based on the live data size. It emphasizes the importance of garbage collection logging for performance analysis.
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淺談 Java GC 原理、調教和 新發展
- 1. 淺談 Java GC 原理、調教和 新發展 LeonChen 陳逸嘉 Java Architect 文曄科技
- 2. 陳逸嘉 (Leon Chen) • Master of NTHU CS • More than 15 years in Java/JEE, as programmer, architect, developer leader and consultant, in finance/telecom domain. • 工研院 • 得捷 • 新光人壽 • Ericsson • Oracle • 文曄科技 (WT Microelectronics) 2
- 3. 著作 • TW Patent 182927, 一種文章切割方法, 2003, 陳逸嘉, 林一中 • TW Patent 206819, 自動服務組合方法及系統, 2004, 陳逸嘉, 許維德, 洪 鵬翔 • US Patent 7,617,174, Method and system for automaRc service composiRon, 2009, Leon Chen, Wei-‐Tek Hsu, Peng-‐Hsiang Hung 3
- 4.
- 5. Performance Impact of GC 5 Java SE 6 HotSpot[tm] Virtual Machine Garbage CollecRon Tuning h[p://www.oracle.com/technetwork/java/javase/gc-‐tuning-‐6-‐140523.html 0.6 0.2 8 32
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- 15. JAVA HEAP STRUCTURE AND GC 15
- 16. Hotspot JVM Heap Layout 16 Young Old (Tenured) Permanent Eden From To Survivor Spaces NaRve -‐Xms -‐Xmx -‐XX:PermSize -‐XX:MaxPermSize NO
- 17. GC Fundamentals Garbage DistribuRon – Objects die young 17
- 18. 18 GC Fundamentals Garbage DistribuRon – Objects die young
- 19. Minor GC (Young GeneraRon GC) 19 Young Old Eden From To Survivor Spaces
- 20. Minor GC (Young GeneraRon GC) 20 Young Old Eden From To Survivor Spaces ! ! !! ! ! !
- 21. Minor GC (Young GeneraRon GC) 21 Young Old Eden From To Survivor Spaces 1 1 1
- 22. Minor GC (Young GeneraRon GC) 22 Young Old Eden To From Survivor Spaces 1 1 1
- 23. Minor GC (Young GeneraRon GC) 23 ! Young Old Eden To From Survivor Spaces ! ! ! ! ! ! ! 1 ! 1 1 1
- 24. Minor GC (Young GeneraRon GC) 24 Young Old Eden To From Survivor Spaces 1 2 1 2
- 25. Minor GC (Young GeneraRon GC) 25 Young Old Eden From To Survivor Spaces 1 2 1 2
- 26. Minor GC (Young GeneraRon GC) 26 Young Old Eden From To Survivor Spaces 16 1 16 2 ! ! ! ! ! ! ! ! 16 16 Promo
- 27. Minor GC (Young GeneraRon GC) 27 Young Old Eden To From Survivor Spaces 17 17 1 2 1 3
- 28. Major GC (Old GeneraRon GC, Full GC) 28 Young Old Eden To From Survivor Spaces
- 29. Major GC (Old GeneraRon GC, Full GC) 29 Young Old Eden To From Survivor Spaces ! ! !! !
- 30. Major GC (Old GeneraRon GC, Full GC) 30 Young Old Eden To From Survivor Spaces Compact
- 31. Tuning Guideline • 讓 heap 的 size 足以容納程式的一般運作 • Major GC 通常會比 Minor GC 花更多的時間 • 盡可能減少 Major GC 的次數 31
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- 33. 33 花太多時間做 GC →Performance變慢 Performance變慢→花太多時間做 GC 不一定!!!
- 34. Performance Tuning Methodology 34 Advanced JVM Tuning; Java One 2011; David Keenan, Monica Beckwith
- 35. GC Logging in ProducRon • Don’t be afraid to enable GC logging in producRon – Very helpful when diagnosing producRon issues • Extremely low / non-‐existent overhead – Maybe some large files in your file system. – We are surprised that customers are sRll afraid to enable it 35
- 36. 36 If Someone doesn’t enable GC logging in producEon I shoot them!
- 37. Most Important GC Logging Parameters • You need at least: – -‐XX:+PrintGCDetails – -‐XX:+PrintGCTimeStamps • Add -‐XX:+PrintGCDateStamps if you must know the Rme • Also useful – -‐Xloggc:file – Rotate GC Log, Aqer Java 1.6_34 (or 1.7_2): -‐XX:+UseGCLogFileRotaRon -‐XX:NumberOfGCLogFiles=5 -‐XX:GCLogFileSize=10M 37
- 38. GCViewer – Offline analysis of GC logs h[ps://github.com/chewiebug/GCViewer 38
- 39. GCViewer – Memory Leak Pa[ern 39
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- 42. Hotspot Tuning -‐ Sizing Heap • Young GeneraRon size determines • Frequency of minor GC • Number of objects reclaimed in minor GC • Old GeneraRon Size • Should hold applicaRon's steady-‐state live data size • Try to minimize frequency of major GC’s • JVM footprint should not exceed physical memory • Max of 80-‐90% RAM (leave room for OS) • Thumb Rule: Try to maximize objects reclaimed in young gen. Minimize Full GC frequency 42
- 43. Calculate Live DataSize (LDS) • 經過 full GC 後, 所剩下的 heap size • Make sure you get full GCs during steady-‐state • Induce a couple if necessary – JConsole / VisualVM – jmap -‐histo:live pid – System.gc • Remove it before deployment. :-‐) 43
- 44. Calculate Live Data Size • GC log example: 44
- 45. Calculate Live Data Size by GCViewer 45
- 46. IniRal Heap ConfiguraRon • Rule of thumb – Set -‐Xms and -‐Xmx to 3x to 4x LDS – Set both -‐XX:PermSize and -‐XX:MaxPermSize to around 1.2x to 1.5x the max perm gen size – Set the generaRon sizes accordingly • Young gen should be around 1x to 1.5x LDS • Old gen should be around 2x to 3x LDS • e.g., young gen should be around 1/3-‐1/4 of the heap size 46
- 47. Hotspot JVM Heap Layout 47 Young –Xmn768m Old (Tenured) Permanent NaRve -‐Xms2g –Xmx2g -‐XX:PermSize -‐XX:MaxPermSize For LDS of 512m : -‐Xmn768m -‐Xms2g -‐Xmx2g
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- 49. High Throughput vs. Low Latency 49 High Throughput Low Latency App Thread GC Thread 專心 分心 較低 較高 較長 較短 Stop the world Total Cost
- 50. High Throughput vs. Low Latency • For most applicaRons, GC overhead is small – 2% – 5% • High Throughput GCs – Move most work to GC pauses – ApplicaRon threads do as li[le as possible – Least overall GC overhead • Low Latency (Pause) GCs – Move work out of GC pauses – ApplicaRon threads do more work • Bookkeeping for GC more expensive – More overall GC overhead 50
- 51. ApplicaRon Requirement • Different applicaRons have different requirements – Higher Throughput: • Batch processing • Web applicaRon: pauses during garbage collecRon may be tolerable, or simply obscured by network latencies – Lower Latencies: • InteracRve graphics applicaRon 51
- 52. HotSpot Garbage Collectors in Java SE 6 52 G1 -XX:+UseSerialGC -XX:+UseConcMarkSweepGC -XX:+UseParallelOldGC -XX:+UseParallelGC -‐XX:+UseParNewGC
- 53. HotSpot Garbage Collectors in Java SE 6 53 G1 -XX:+UseSerialGC -XX:+UseConcMarkSweepGC -XX:+UseParallelOldGC -XX:+UseParallelGC -‐XX:+UseParNewGC
- 54. Serial Collector 54 App Thread GCThread stop-‐the-‐world pause Serial Collector
- 55. HotSpot Garbage Collectors in Java SE 6 55 G1 -XX:+UseSerialGC -XX:+UseConcMarkSweepGC -XX:+UseParallelOldGC -XX:+UseParallelGC -‐XX:+UseParNewGC
- 56. Serial VS Parallel Collector 56 App Thread GC Thread stop-‐the-‐world pause Serial Collector Parallel Collector
- 57. HotSpot Garbage Collectors in Java SE 6 57 G1 -XX:+UseSerialGC -XX:+UseConcMarkSweepGC -XX:+UseParallelOldGC -XX:+UseParallelGC -‐XX:+UseParNewGC
- 58. CMS Collector 58 App Thread GCThread iniRal mark concurrent marking remark concurrent sweeping
- 59. CMS Collector with ParNewGC 59 App Thread GC Thread
- 60. GC SuggesRons 60 Low Latency Collectors Throughput Collectors GeneraRon Young Old 2+ CPUs -XX:+UseParNewGC 2+ CPUs -XX:+UseParallelGC -XX: +UseConcMarkSweepGC -XX:+UseParallelOldGC New G1 Collector as of WLS10.3.1/JDK 6 Update 14
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- 62. Problems of Current GC • Memory is cheaper and cheaper • 64 bits JVM • We can use very large heap! Young Old How to handle large heap size?
- 63. G1 Collector • The Garbage-‐First Collector – Since JDK 6u14, officially supported as of JDK 7u4 – -‐XX:+UseG1GC – Future CMS Replacement – Server “Style” low latency collector • Parallel • Concurrent – GeneraRonal – Good Throughput – CompacRng – Improved ease-‐of-‐use – Predictable (Soq Real-‐Time) 63
- 64. G1 – Heap Layout 64 S S Old Eden S Survivor Free Region Type
- 65. CMS vs G1 Collectors 65 • Heap split into regions • Young generaRon (A set of regions) • Old generaRon (A set of regions)
- 66. G1 Collector: Parallelism Concurrency 66 App Thread GC Thread
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- 70.
- 71. 什麼時候該使用G1? • Large heaps – Typically ~6GB or larger heaps • ApplicaRons that needs low pauses 71
- 72. 什麼時候不該使用 G1? • G1需要更多的compuRng resources和 memory 來運行 • No large heaps – Typically smaller than 6GB • ApplicaRons that don’t need low pauses 72
- 73.
- 74. Summarize • Professional developer 必須非常了解 variables, objects 的 life cycle, objects 何時有 資格被會收 • GC will hurt system performance • Must monitor GC acRviRes • Must enable GC logging
- 75. Tuning Procedures • Observer LDS to decide iniRal size se~ng • Use parallel GC first • If the GC pause Rme can’t be accepted, then trying to use CMS • If heap is over 6G, and look for lower down pause Rme, you can consider G1 • Monitoring -‐ Analyzing -‐ Tuning -‐ Monitoring -‐ … 75
- 76.
- 77. References • Step-‐by-‐Step: Garbage CollecRon Tuning in the Java HotSpot™ Virtual Machine – JavaOne 2010 • The Garbage CollecRon Mythbusters – JavaOne 2010 • GC Tuning for the HotSpot JVM – JavaOne 2009 • uPortal Performance OpRmizaRon. Faizan Ahmed. Architect and Engineering Group. Enterprise Systems Services. RUTGERS. faizan@rutgers.edu. • h[p://java.sun.com/javase/technologies/hotspot/gc/ gc_tuning_6.html
- 78. • Java Performance – Charlie Hunt, Binu John • HotSpot GC Tuning Guide for Java SE 6 h[p://www.oracle.com/technetwork/java/javase/gc-‐ tuning-‐6-‐140523.html • Memory Management in the Java HotSpot VM h[p://www.oracle.com/technetwork/java/javase/ memorymanagement-‐whitepaper-‐150215.pdf • Java 6 Performance Whitepaper h]p://java.sun.com/performance/reference/whitepapers/6_performance.html 78
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