Too many (handled?) QuicException instances on HTTP/3 server side

[ladeak]

I am investigating a performance related issue on an API using Quic (HTTP/3 on server side).

I think this is unrelated to my issue directly, but I happened to notice a lot of instances of QuicException -s generated even when there is seemingly no exceptions.

Description

Besides QuicExceptions, there are many-many instances of ResettableTaskSource and System.Net.Quic.ValueTaskSource

The above perf session was captured on an HTTP/3 endpoint where a single client sent 20 000 requests to the same endpoint (which endpoint in asp.net core happened to just return "OK"), without request body and without response body.

Configuration

.NET 10, Windows 11, x64

Regression?

Probably not.

Analysis

No analysis yet, but my expectation would be no quic exceptions to be instantiated (given the exception is not thrown or handled anyway). To my current understanding these quic exceptions are not handled by ASP.NET Core, nor the consuming application, so it seems to only exists in System.Net.Quic?

[wfurt]

This will be hard to investigate without some repro code @ladeak.

[ladeak]

Minimal repro for the server:

using System.Text.Json.Serialization;

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.MapGet("/", async context =>
{
    context.Response.Headers.TryAdd("x-custom", new Microsoft.Extensions.Primitives.StringValues("test"));
    await context.Response.WriteAsync("Hello World " + context.Request.Protocol.ToString());
});

appsettings.json:

{
  "Kestrel": {
    "EndpointDefaults": {
      "Protocols": "Http1AndHttp2AndHttp3"
    }
  },
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "AllowedHosts": "*"
}

And invoke this endpoint using HTTP/3 version from a single client many times.

[wfurt]

That is only one side. How is the client managing connections? And is there gracefully shutdown..? And let say, you do 10 rounds. Do you see the same exception e.g. is this load specific or is there something about the setup ?

[ladeak]

I used the built in HttpClient with for loop to send the GET requests, pretty standard code. With 10 requests, I see no exceptions:

Right after I send exactly the same request, but 20_000 times (without even restarting the server between the tests):

The requests are non-concurrent and they use the same QUIC connection. I am running on my localhost machine.

[wfurt]

Quic is sensitive to load but that should not be problem IMHO for sequential send. I'm, curious it can be related to port allocation. And You create the HttpClient once outside of the loop and use the SendAsync/GetAsync?

[ladeak]

And You create the HttpClient once outside of the loop and use the SendAsync/GetAsync?

Yes

[ladeak]

Also I don't see anything under the exceptions for this process:

[rzikm]

Also I don't see anything under the exceptions for this process:

That means that the exception is not thrown, only allocated. The number of exceptions seems to be the same as the number of ValueTaskSources, so these are likely the exceptions that we set to signal that the stream has been closed. Do you have any evidence of impacting your scenario outside of (mildly) increasing GC pressure?