Overview

The .NET Garbage Collector (GC) is a fully managed, generational, mark‑and‑sweep collector that automatically reclaims memory used by your applications. It runs concurrently with the managed threads and strives to keep pause times low while maximizing throughput.

Generations

Objects start in Generation 0. If they survive a collection they are promoted to higher generations.

• Gen 0 – Short‑lived objects, collected frequently.
• Gen 1 – Medium‑lived objects, promotion after surviving Gen 0.
• Gen 2 – Long‑lived objects, collected less often.
• LOH – Large objects allocated directly in a separate heap.

+-----------------------+
|      Managed Heap     |
| +---+ +---+ +-------+ |
| |G0 | |G1 | |  G2   | |
| +---+ +---+ +-------+ |
| +-------------------+ |
| |  Large Object Heap | |
| +-------------------+ |
+-----------------------+

Configuration

Control GC behavior via runtimeconfig.json or programmatically.

{
  "runtimeOptions": {
    "configProperties": {
      "System.GC.Server": true,
      "System.GC.RetainVM": false,
      "System.GC.HeapCount": 4
    }
  }
}

Programmatic example:

using System;
using System.Runtime;

GCSettings.LatencyMode = GCLatencyMode.LowLatency;
// …run critical section…
GCSettings.LatencyMode = GCLatencyMode.Interactive;

Diagnostics & Monitoring

Use built‑in tools to monitor GC activity.

• dotnet-counters – Real‑time counters.
• dotnet-trace – Event tracing of GC events.
• dotnet-gcdump – Capture heap snapshots.
• Performance Counters – GCHeapSize, Gen 0 Collections, etc.

# Sample: dotnet-counters monitor
dotnet-counters monitor -p <pid> System.Runtime

FAQ