A Garbage Collector (GC) is like an automatic housekeeper for a program’s memory. It cleans up memory that’s no longer being used, which saves developers from doing it manually and prevents a lot of tricky bugs.
🏠 The GC’s Room vs. The Whole House
Think of a program’s total memory as a house:
| Part of the House | What it Represents |
|---|---|
| GC Heap (the main room) | Memory managed by the GC, where most of the activity (memory usage) happens. |
| Other Rooms | Memory needed for other things, like program code and system components. |
Tip
To locate a memory problem:
- If GC Heap ≈ Total Memory Usage → the issue is with objects the GC is managing.
- Otherwise → the problem lies elsewhere in the house.
🧹 The Smart Housekeeper
The GC acts like a housekeeper who manages your apartment (the program) but also pays attention to the entire building (the computer’s RAM).
- Normal Mode → follows a regular cleaning schedule.
- Aggressive Mode → kicks in when RAM is running low:
- Performs a full blocking GC (a deep clean).
- Frees as much memory as possible to avoid paging.
📊 Key Details
| Aspect | Explanation |
|---|---|
| When does it get aggressive? | A high memory load situation is when RAM usage hits: - 90% on machines with < 80 GiB RAM - 90–97% on larger machines |
| Is this adjustable? | Yes. Threshold can be changed: - React sooner → smaller memory footprint. - React later → fine if the program is small. |
| Containers? | In a container, the GC only watches the container’s memory limit (its own water supply), not the whole machine. |
Abstract
Big Picture
The GC isn’t just cleaning up after your program.
It adapts its behavior depending on how much memory your program and the whole system are using.
📌 Visual Analogy (Mermaid Diagram)
flowchart TD A[Program Memory - House] --> B[GC Heap - Main Room] A --> C[Other Rooms - Code and System Components] B --> D[Normal Mode Cleaning] B --> E[Aggressive Mode - Full Blocking GC] E --> F[Free Up Memory to Prevent Paging]