Garbage Collection: .NET vs Go

Overview

• Introduction
• .NET Garbage Collection
• How it works:
• Advantages of Generational GC:
• Additional .NET GC Features:
• Go Garbage Collection
• Key Differences

Introduction

Both .NET and Go employ automatic memory management through garbage collection (GC), but their approaches differ significantly.

.NET Garbage Collection

.NET uses a generational, mark-and-compact collector:

Generational Garbage Collection in .NET

.NET's garbage collector is based on the generational hypothesis, which states that most objects have short lifetimes. The GC divides objects into three generations:

1. Generation 0 (Gen 0):
   • The youngest generation.
   • All new objects start here.
   • Collected most frequently.
   • Very fast and efficient for short-lived objects.
2. Generation 1 (Gen 1):
   • Objects that survive a Gen 0 collection are promoted here.
   • Serves as a buffer between short-lived and long-lived objects.
   • Collected less frequently than Gen 0.
3. Generation 2 (Gen 2):
   • The oldest generation.
   • Contains long-lived objects.
   • Collected least frequently.
   • Full collection of Gen 2 is the most expensive operation.

How it works:

• When Gen 0 fills up, a garbage collection is triggered.
• If objects in Gen 0 survive, they're moved to Gen 1.
• If Gen 1 fills up, both Gen 0 and Gen 1 are collected.
• Objects surviving from Gen 1 are moved to Gen 2.
• When Gen 2 fills up, a full garbage collection occurs (all generations).

Advantages of Generational GC:

• Efficient for applications with many short-lived objects.
• Reduces the work done in most collections by focusing on younger generations.
• Allows for different collection strategies for different generations.

Additional .NET GC Features:

• Mark-and-Compact: Live objects are marked and compacted to reduce fragmentation.
• Concurrent: Recent versions support background GC to minimize pauses.
• Workstation vs. Server: Different GC strategies for different application types.

.NET's GC is highly tunable, with options for concurrent, background, and incremental collection.

Go Garbage Collection

Go employs a concurrent, tri-color mark-and-sweep collector:

• Concurrent: GC runs concurrently with the application, reducing pause times.
• Non-generational: All objects are treated equally, regardless of age.
• Mark-and-Sweep: Live objects are marked; unmarked objects are swept (freed).
• Write Barrier: Ensures consistency during concurrent collection.

Go's GC prioritizes low latency over maximum throughput, aiming for sub-millisecond pause times.

Key Differences

1. Generational Approach: .NET uses generations, Go doesn't.
2. Compaction: .NET compacts memory; Go doesn't, potentially leading to fragmentation.
3. Tuning: .NET offers more tuning options; Go's GC is simpler with fewer knobs.
4. Pause Times: Go generally achieves shorter pause times.
5. Memory Overhead: .NET's GC can use more memory due to its generational nature.

Both systems continue to evolve, with ongoing research and improvements focused on reducing pause times and improving overall performance.

Comparison