ASP.NET Core：使用开发环境变量的非常慢（第一）页面加载时间

Question

My ASP.NET Core application went very slow on debugging from one day to another. It tooks up to 90 seconds to load a single site, which was loaded in max 5-6 seconds before at the first request. I didn't made any changes which could explain this. I tried different things to find out why. It seems that the slowdown-process begins with the request.

I found out that this is only the case when I set the ENVIRONMENT variable in the project options under debugging to Development . For testing I set it to Production and surprisingly my APP was pretty fast like before this issue. I could only find the pre-generated part from the example where the variable is checked:

if (env.IsDevelopment()) {
            app.UseDeveloperExceptionPage();
            app.UseBrowserLink();
            DebugData.InsertIfMissing(); // This is from me and inserts some testdata in the db
        } else {
            app.UseExceptionHandler("/Home/Error");
        }

But although I commented those lines out, my ASP.NET Core application is stil very slow when setting ENVIRONMENT=Development. I have no idea why. I could only explain this with the theory that ASP.NET Core, EF Core or other parts of the framework check the variable internally and do something which requires much time when in development-environment.

For now its a acceptable workaround to use the production environment. But on the long run I would like to use this nice variable to do some things only in development like filling the database with some test-data. What can be the reason for this performance problem in dev-mode?

The output of the webserver says:

Hosting environment: Development
Content root path: C:\Dev\MyApp
Now listening on: http://localhost:5000
Application started. Press Ctrl+C to shut down.
info: Microsoft.AspNetCore.Hosting.Internal.WebHost[1]
      Request starting HTTP/1.1 GET http://localhost:5000/
info: Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker[1]
      Executing action method MyApp.Controllers.HomeController.Index (MyApp) with arguments () - ModelState is Valid
info: Microsoft.AspNetCore.Mvc.ViewFeatures.Internal.ViewResultExecutor[1]
      Executing ViewResult, running view at path /Views/Home/Index.cshtml.
info: Microsoft.Extensions.DependencyInjection.DataProtectionServices[0]
      User profile is available. Using 'C:\Users\MyUserName\AppData\Local\ASP.NET\DataProtection-Keys' as key repository and Windows DPAPI to encrypt keys at rest.
info: Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker[2]
      Executed action MyApp.Controllers.HomeController.Index (MyApp) in 84836.6896ms

As you can see its not a startup problem, because it tooks most of the time for executing the action. But the action of the home-controller only serves a simple Razor view, not at least a database-connection is created there.

To see how slow this is, here a example of the same request with ENVIRONMENT=Production

info: Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker[2]
      Executed action MyApp.Controllers.HomeController.Index (MyApp) in 2728.3558ms

And the second request, where ASP.NET has most of the things initialized/cached:

info: Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker[2]
  Executed action MyApp.Controllers.HomeController.Index (MyApp) in 19.3621ms

Answer 1

I found out that this was not directly related to ASP.NET Core. Instead, the microsoft symbol-servers were enabled in the debug-settings on options > debugging > symbols:

This made Visual Studio to load the symbols of all microsoft assemblys. It seems that the symbol-cache was not persistent cause it was stored in a temp folder. So VS reload them from time to time, which result in obvious performance issues. I disabled them and now the development-area is nearly as fast as production.