Garbage Collection.

Transcription

1 Garbage Collection

2 Why GC Is Important?

3 Memory and External Resources Stack Unmanaged Heap Managed Heap External Resources Mutex File Socket Bitmap......

4 Comparison Stack Speed Of Allocation Speed Of Execution Managed Heap Powerful Care-Free Unmanaged Heap Security

5 Object Lifecycle Instance Method alloc Memory Allocated.ctor() Initialized reclaim Finalize() Memory Reclaimed reclaim External Resources Released

6 Object in Heap Managed Heap.NET CLR / Java VM Internal Data Structure Type Info Ptr Sync Block Index Type Descriptor of Class A Type Descriptor of Class C Type Descriptor of Class B... Fields in the Parent Fields in the Object Sync Block Cache Sync Block #0 Sync Block #1 Sync Block #2...

7 NextObjPtr

8 A NextObjPtr

9 A B NextObjPtr

10 A B C NextObjPtr

11 A B C D NextObjPtr

12 A B C D E NextObjPtr

13 A B C D E F NextObjPtr

14 A B C D E F G NextObjPtr

15 A B C D E F G H NextObjPtr

16 A B C D E F G H I NextObjPtr

17 A B C D E F G H I J NextObjPtr

18 A B C D E F G H I J NextObjPtr

19 Roots A B C D E F G H I J NextObjPtr

20 Roots A B C D E F G H I J NextObjPtr

21 Roots A B C D E F G H I J NextObjPtr

22 Roots A B C D E F G H I J NextObjPtr

23 Roots A B C D E F G H I J NextObjPtr

24 Roots A B C D E F G H I J NextObjPtr

25 Roots A B C D E F G H I J NextObjPtr

26 Roots A B C D E F G H I J NextObjPtr

27 Roots A C D F H J NextObjPtr

28 Roots A C D F H J NextObjPtr

29 Roots A C D F H J NextObjPtr

30 Roots A C D F H J NextObjPtr

31 Roots A C D F H J NextObjPtr

32 Roots A C D F H J NextObjPtr

33 A C D F H J K NextObjPtr

34 What s Roots Internal Data Structure Stack Type Descriptor of Class A... Starting Offset 0x x x D Ending Offset 0x x C 0x Roots this, arg1, ECX, EDX this, myobj myobj

35 Infant Mortality

36 Generation 0 A B C D E

37 Generation 1 Generation 0 A B D

38 Generation 1 Generation 0 A B D F G H I J K

39 Generation 1 Generation 0 A B D F G I K

40 Generation 1 Generation 0 A B D F G I K

41 Generation 1 Generation 0 A B D F G I K L M N O

42 Generation 1 Generation 0 A B D F G I K N O

43 Generation 1 Generation 0 A B D F G I K N O P Q R S

44 Generation 2 Generation 1 Generation 0 D F I N O Q S

45 Monitoring.NET GC Using PerfMon

46 Java Generational GC

47 JVM Memory Ratio

48 JVM Switches for Memory Ratio -XX:MinHeapFreeRatio=40 -XX:MaxHeapFreeRatio=70 -Xms=3670k -Xmx=64m -XX:NewRatio=8 -XX:NewSize=2228k -XX:MaxNewSize=unlimited -XX:ServivorRatio=32 -XX:PermSize=4m

49 Performance Considerations Throughput Pause Footprint Promptness

50 Choose A GC Collector Default Collector Throughput Collector (Parallel Collector) -XX:+UseParallelGC (Parallel Collector + Default Collector) -XX:ParallelGCThreads=<desired number> -XX:+UseAdaptiveSizePolicy Concurrent Low Pause Collector -XX:+UseConcMarkSweepGC (Default Collector + Concurrent Collector) -XX:+UseConcMarkSweepGC -XX:+UseParNewGC (Parallel Collector + Concurrent Collector) Incremental Low Pause Collector (Train Collector) -Xincgc

51 Related JVM Switches -XX:+AggressiveHeap (when physical memory > 256M) -Xmixed -Xint (-nojit) -Xloggc:<file> -Xms<size> -Xmx<size> -Xss<size> -Xnoclassgc -Xbatch -server -client -XX:+DisableExplicitGC

52 -verbose:gc JVM Switches for GC Portal -XX:+PrintGCTimeStamps -XX:+PrintGCDetails -XX:+PrintTenuringDistribution

53 -verbose:gc The verbose:gc logs contain valuable information about: GC pause times Frequency of GC Application run times Size of objects created and destroyed Rate of object creation Memory recycled at each GC

54 Information Derived from verbose:gc Logs Average GC pauses in the young and old generation Average GC frequency in the young and old generation GC sequential overhead GC concurrent overhead Memory recycled by each GC in the young and old generation Allocation rate Promotion rate Total data allocated by the application Total data can be split into short term data and long term data Short term data Total active data Memory leaks

55 GC Portal Design GC Portal Analyzer and Reporting Engine Graphical Engine Intelligence Engine Session and Storage Engine

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60 Install The GC Portal Step 1 - Download the GC Portal software. Step 2 - Extract the GC Portal software from the archive. Step 3 - Install and configure the Sun ONE Application Server. Step 4 - Install and configure awk and Perl for Windows. Step 5 - Set up the GC Portal database. Step 6 - Start the Sun ONE Application Server. Step 7 - Deploy GC Portal on Sun ONE Application Server. Step 8 - Configure the GC Portal. Step 9 - Install the third party software from KavaCharts for charting graphs. Step 10 - Run the GC Portal.

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