Background GC vs. Blocking GC

The Garbage Collector (GC) has two primary strategies for a full Gen 2 cleanup.
The choice depends on the situation: application responsiveness vs. maximum memory reclamation.

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Background GC (BGC): The Quiet Housekeeper 🤫

• Analogy: A quiet housekeeper tidying the office while everyone is still working.
• Goal: Maintain application responsiveness.
• Method:
  • Only sweeps, does not compact.
  • Creates a free list of available memory spaces.
• Outcome: Minimal interruption; some fragmentation remains.

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Full Blocking GC: The Emergency Crew 🚨

• Analogy: “All hands on deck” cleanup — everything pauses while the GC works.
• Goal: Reclaim maximum memory.
• Method:
  • Compacts the heap aggressively.
  • Pauses the entire application (Stop-the-World).
• Used When:
  1. High Memory Pressure – system RAM is low.
  2. Severe Fragmentation – sweeping alone isn’t enough.
  3. Last Resort – just before throwing an OutOfMemoryException.

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Diagram: Cleaning Strategy Choice

flowchart TB
    A[Full Gen 2 Cleanup Needed] -->|Default| B[Background GC - BGC]
    A -->|Critical Situation| C[Full Blocking GC]

    B --> D[Sweeps Only]
    B --> E[Free List Created]
    C --> F[Compacts Heap]
    C --> G[Application Paused]