How does ASP.NET Core handle garbage collection

ASP.NET Core relies on the .NET runtime for garbage collection (GC). The .NET runtime includes a high-performance, automatic garbage collector designed to manage memory efficiently and to improve application performance. Here’s how ASP.NET Core handles garbage collection through the .NET runtime:

Key Features of .NET Garbage Collection

1. Automatic Memory Management:

   • The garbage collector automatically frees memory that is no longer in use, eliminating the need for manual memory management and reducing memory leaks.

2. Generational GC:

   • The .NET garbage collector uses a generational approach, dividing objects into three generations (Gen 0, Gen 1, and Gen 2) based on their lifetimes.
   • Gen 0: Short-lived objects. Most objects are expected to be short-lived, so they are initially allocated in Gen 0.
   • Gen 1: Medium-lived objects. Objects that survive a Gen 0 collection are promoted to Gen 1.
   • Gen 2: Long-lived objects. Objects that survive a Gen 1 collection are promoted to Gen 2. This generation is collected less frequently.

3. Concurrent and Background GC:

   • The garbage collector can perform collections concurrently with the application, minimizing pauses.
   • Background GC: A concurrent GC mode that allows for background collection of Gen 2 objects, improving performance by reducing the impact of garbage collection on application throughput.

4. Large Object Heap (LOH):

   • Large objects (greater than 85,000 bytes) are allocated in a separate heap called the Large Object Heap (LOH). The LOH is collected less frequently because it is more expensive to collect.

5. Ephemeral Segment:

• Small objects are allocated in the ephemeral segment, which includes Gen 0 and Gen 1. This segment is designed to optimize allocation and collection performance for short-lived objects.

Garbage Collection in ASP.NET Core

ASP.NET Core applications benefit from the garbage collection features provided by the .NET runtime. The garbage collector works in the background, freeing up memory and optimizing performance without requiring explicit intervention from developers.

Configuration and Tuning

While the garbage collector works well out of the box, there are scenarios where developers might want to configure or tune GC settings to optimize performance for specific workloads. Here are some options available for tuning garbage collection in ASP.NET Core:

1. GC Modes:

   • Workstation GC: Optimized for desktop applications, providing low latency.
   • Server GC: Optimized for server applications, providing high throughput. This is the default mode for ASP.NET Core applications running on servers.

2. GC Configuration Settings:

   • gcServer: Setting this to true enables server garbage collection.
   • gcConcurrent: Enables or disables concurrent garbage collection.
   • gcAllowVeryLargeObjects: Allows allocation of arrays that are larger than 2 GB on 64-bit platforms.

   These settings can be configured in the runtimeconfig.json file or through environment variables.

{

  "runtimeOptions": {

    "configProperties": {

      "System.GC.Server": true,

      "System.GC.Concurrent": true

    }

  }

}

3. Environment Variables:

GC settings can also be configured using environment variables, such as COMPlus_gcServer, COMPlus_gcConcurrent, and COMPlus_gcAllowVeryLargeObjects.

4. Monitoring and Diagnostics:

ASP.NET Core provides several tools and APIs for monitoring and diagnosing garbage collection performance, including performance counters, dotnet-counters, dotnet-trace, and the EventPipe API.

Best Practices

• Minimize Object Allocations: Reducing the number of allocations can reduce the frequency and cost of garbage collections.
• Pool and Reuse Objects: Use object pooling to reuse objects instead of frequently allocating and deallocating them.
• Avoid Large Object Allocations: Minimize the allocation of large objects to reduce the impact on the LOH.
• Profile and Monitor: Use profiling and monitoring tools to identify and address performance bottlenecks related to garbage collection.

Summary

ASP.NET Core leverages the .NET runtime's advanced garbage collection mechanisms to manage memory efficiently and optimize application performance. While the garbage collector works automatically, developers have several options for configuring and tuning GC settings to meet the specific needs of their applications. By understanding how garbage collection works and following best practices, developers can ensure that their ASP.NET Core applications run efficiently and reliably.