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Contents

Title and Copyright Information

Preface

• Audience
• Documentation Accessibility
• Related Documents
• Conventions

1 Introduction to Garbage Collection Tuning

• What Is a Garbage Collector?
• Why Does the Choice of Garbage Collector Matter?
• Supported Operating Systems in Documentation

2 Ergonomics

• Garbage Collector, Heap, and Runtime Compiler Default Selections
• Behavior-Based Tuning
  • Maximum Pause-Time Goal
  • Throughput Goal
  • Footprint
• Tuning Strategy

3 Garbage Collector Implementation

• Generational Garbage Collection
• Generations
• Performance Considerations
• Throughput and Footprint Measurement

4 Factors Affecting Garbage Collection Performance

• Total Heap
  • Heap Options Affecting Generation Size
  • Default Option Values for Heap Size
  • Conserving Dynamic Footprint by Minimizing Java Heap Size
• The Young Generation
  • Young Generation Size Options
  • Survivor Space Sizing

5 Available Collectors

• Serial Collector
• Parallel Collector
• The Mostly Concurrent Collectors
• Selecting a Collector

6 The Parallel Collector

• Number of Parallel Collector Garbage Collector Threads
• Arrangement of Generations in Parallel Collectors
• Parallel Collector Ergonomics
  • Options to Specify Parallel Collector Behaviors
  • Priority of Parallel Collector Goals
  • Parallel Collector Generation Size Adjustments
  • Parallel Collector Default Heap Size
    • Specification of Parallel Collector Initial and Maximum Heap Sizes
• Excessive Parallel Collector Time and OutOfMemoryError
• Parallel Collector Measurements

7 The Mostly Concurrent Collectors

• Overhead of Mostly Concurrent Collectors

8 Concurrent Mark Sweep (CMS) Collector

• Concurrent Mark Sweep Collector Performance and Structure
• Concurrent Mode Failure
• Excessive GC Time and OutOfMemoryError
• Concurrent Mark Sweep Collector and Floating Garbage
• Concurrent Mark Sweep Collector Pauses
• Concurrent Mark Sweep Collector Concurrent Phases
• Starting a Concurrent Collection Cycle
• Scheduling Pauses
• Concurrent Mark Sweep Collector Measurements

9 Garbage-First Garbage Collector

• Introduction to Garbage-First Garbage Collector
• Enabling G1
• Basic Concepts
  • Heap Layout
  • Garbage Collection Cycle
• Garbage-First Internals
  • Determining Initiating Heap Occupancy
  • Marking
  • Behavior in Very Tight Heap Situations
  • Humongous Objects
  • Young-Only Phase Generation Sizing
  • Space-Reclamation Phase Generation Sizing
• Ergonomic Defaults for G1 GC
• Comparison to Other Collectors

10 Garbage-First Garbage Collector Tuning

• General Recommendations for G1
• Moving to G1 from Other Collectors
• Improving G1 Performance
  • Observing Full Garbage Collections
  • Humongous Object Fragmentation
  • Tuning for Latency
    • Unusual System or Real-Time Usage
    • Reference Object Processing Takes Too Long
    • Young-Only Collections Take Too Long
    • Mixed Collections Take Too Long
    • High Update RS and Scan RS Times
  • Tuning for Throughput
  • Tuning for Heap Size
  • Tunable Defaults

11 Other Considerations

• Finalization and Weak, Soft, and Phantom References
• Explicit Garbage Collection
• Soft References
• Class Metadata