Earlier today Sam Saffron from the StackExchange team blogged about the performance of view lookups in MVC. Specifically, he compared referencing a view by name (i.e. calling something like @Html.Partial("_ProductInfo")) and by path (@Html.Partial("~/Views/Shared/_ProductInfo.cshtml")). His results indicate that in scenarios where a page is composed from many views and partial views (for example, when you are rendering a partial view for each item in a list) it’s more efficient to reference your views using the full path instead of just the view name.

I know that bit of code quite well and it seemed strange to me that such a performance difference would exist because view lookups are cached regardless of how you reference them. Specifically, once an application is warmed up both the Razor and WebForms view engines use the lookup parameters to retrieve the cached results. If anything the cache key produced from a view path is usually longer than the one produced from a view name but even that should not have a measurable impact.

While I cannot explain the differences that Sam is seeing (and since I know he is seeing them in production too I’m quite sure he has the application configured correctly for performance testing) I thought this would be a good opportunity to present the basics of MVC view lookup optimizations as well as a few additional techniques that people might not be familiar with.

Hopefully you won’t go replacing all of your view references with full paths. Using view names is still easier and more maintainable. And before you do any perf-related changes you should always measure your application. It might turn out that it is fast enough for your needs already.

Run in Release mode

You should always make sure that your application is compiled in Release mode and that your web.config file is configured with <compilation debug="false" />. That second part is super-important since MVC will not do any view lookup caching if you are running your application in debug mode. This helps when you are developing your application and frequently adding/deleting view files, but it will kill your performance in production.

This might seem like obvious advice, but I have seen even experienced devs get bitten by this.

Use only the View Engines that you need

I’ve mentioned this before but it’s worth repeating. The MVC framework supports having multiple view engines configured simultaneously in your application and will query each in turn when it is trying to find a view. The more you have the longer the lookups will take, especially if the view engine you are using is registered last. In MVC 3 we register two view engines by default (WebForms and Razor) and in all versions you might have installed 3rd party view engine such as Spark on nHaml. There is no reason to pay the performance price for something you are not using so make sure you specify only the view engines you need in your Global.asax file:

protected void Application_Start() {
    ViewEngines.Engines.Clear();
    ViewEngines.Engines.Add(new RazorViewEngine());
    ...
}

Customize the view lookup caching

By default (when running in Release mode, of course) MVC will cache the results of the lookups in the application cache available via HttpContext.Cache. While this cache works great and helps us avoid having to check for view files on disk there is also a cost associated with using it (this includes the cost of a thread-safe lookup as well as all the additional cache management such as updating entry expiration policies and performance counters).

To speed things up you could introduce a faster cache in front of the application cache. Fortunately all view engines deriving from VirtualPathProviderViewEngine (that includes WebForms and Razor) have an extensibility point via the settable ViewLocationCache property.

So we can create a new class that implements the IViewLocationCache interface:

public class TwoLevelViewCache : IViewLocationCache {
    private readonly static object s_key = new object();
    private readonly IViewLocationCache _cache;

    public TwoLevelViewCache(IViewLocationCache cache) {
        _cache = cache;
    }

    private static IDictionary<string, string> GetRequestCache(HttpContextBase httpContext) {
        var d = httpContext.Items[s_key] as IDictionary<string, string>;
        if (d == null) {
            d = new Dictionary<string, string>();
            httpContext.Items[s_key] = d;
        }
        return d;
    }

    public string GetViewLocation(HttpContextBase httpContext, string key) {
        var d = GetRequestCache(httpContext);
        string location;
        if (!d.TryGetValue(key, out location)) {
            location = _cache.GetViewLocation(httpContext, key);
            d[key] = location;
        }
        return location;
    }

    public void InsertViewLocation(HttpContextBase httpContext, string key, string virtualPath) {
        _cache.InsertViewLocation(httpContext, key, virtualPath);
    }
}

and augment our view engine registration in the following way:

protected void Application_Start() {
    ViewEngines.Engines.Clear();
    var ve = new RazorViewEngine();
    ve.ViewLocationCache = new TwoLevelViewCache(ve.ViewLocationCache);
    ViewEngines.Engines.Add(ve);
    ... 
}

This TwoLevelViewCache will work best in views that call the same partial multiple times in a single request (and should hopefully have minimum impact on simpler pages).

You could go even further and instead of the simple dictionary stored in httpContext.Items you could use a static instance of ConcurrentDictionary<string, string>. Just remember that if you do that your application might behave incorrectly if you remove or add view files without restarting the app domain.

Over the last few years the ASP.NET team has been including more and more libraries into the various project templates that we ship with Visual Studio and other products. The latest MVC 3 templates come with jQuery, jQuery UI, jQuery Validation, Modernizr, and Entity Framework. All this built-in functionality is great but one remaining snag is that upgrading all the packages by hand can be a pain. Of course the NuGet package manager is an excellent tool that solves the package upgrade problem but so far having project templates with preinstalled NuGet packages was not possible.

This post describes a new feature that will be shipping in NuGet 1.5: preinstalled NuGet packages. Since it is not documented anywhere at this time the purpose of this post is to describe how to create a VS project template with NuGet packages. If you play around with it please also provide feedback so we can make changes/improvements.

Authoring VS project templates is out of scope of this article but you can read more on how to create a project template directly using Visual Studio or using the Visual Studio SDK.

Adding packages to a project templates

NuGet 1.5 is not out yet but the feature has already been checked in and you can try it out by grabbing a recent NuGet preview build and installing the Visual Studio add-in (note that you might have to remove the previous version via the Extension Manager first).

Preinstalled packages work using project template wizards. A special wizard gets invoked when the project gets instantiated. The wizard loads the list of packages that need to be installed and passes that information to the appropriate NuGet APIs. The project template needs to specify where to find the package nupkg files. Currently two package repositories are supported:

1. Packages embedded inside of a VSIX package.
2. Packages embedded inside of the project template itself.

A frequent question is why not support downloading the nupkg files directly from http://nuget.org. We decided not to support such an option because users expect project templates to instantiate quickly and downloading files from the internet would slow things down. Also, it would not work on a plane or in other situations where a connection is not available.

To add preinstalled packages to your project template you need to:

1. Edit your vstemplate file and add a reference to the NuGet template wizard by adding a WizardExtension element:

   <WizardExtension>
       <Assembly>NuGet.VisualStudio.Interop, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null</Assembly>
       <FullClassName>NuGet.VisualStudio.TemplateWizard</FullClassName>
   </WizardExtension>

   NuGet.VisualStudio.Interop.dll is a new assembly that only contains the TemplateWizard class. This class is a simple wrapper that calls into the actual implementation that lives in NuGet.VisualStudio.dll. The assembly version will never change so that project templates continue to work with new versions of NuGet.
2. Add the list of packages to install in the project:

   <WizardData>
       <packages>
           <package id="jQuery" version="1.4.4" />
       </packages>
   </WizardData>

   You can of course add multiple <package> elements. Both the id and version attributes are required. You will notice that this means that a specific version of a package will be installed, even if a newer version is available in the online package feed. We cannot just update to the latest version because a future version of a package might introduce incompatibilities that would break an older version of the project template. It is up to the developer to upgrade using the package manager.

The remaining step is to specify the repository where NuGet can find the package files. As mentioned earlier, two package repository modes are supported:

VSIX package repository

The approach I recommend for deploying Visual Studio project templates is through a VSIX package (read more about VSIX deployment here). The VSIX method is preferable because it allows you to package multiple project templates together and allows developers to easily discover your templates using the VS Extension Manager or the Visual Studio Gallery. On top of that you can easily push updates to your users using the Extension Manager automatic update mechanism.

1. To specify a VSIX as a package repository you modify the <package>element:

   <packages repository="extension"
             repositoryId="MyTemplateExtension.46431780-a0c7-44e0-83c7-5dbd985f8e49">
       ...
   </packages>

The repository attribute specifies the type of repository (“extension”) while repositoryId is the unique identifier of your VSIX (i.e. the value of the ID attribute in the extension’s vsixmanifest file).

You need to add your nupkg files as custom extension content and ensure that they are located under a folder called Packages within the VSIX package. You can place the nupkg files in the same VSIX as your project templates or you can have the packages be located in a separate VSIX if that makes more sense for your scenario (just note that you should not reference VSIXs you do not have control over since they could change in the future and your project templates would break).

Template package repository

If packaging multiple projects is not important to you (e.g. you’re only distributing a single project template), a simpler but also more limited approach is to include the nupgk files in the project template zip file itself.

However, if you are bundling a set of project templates that relate to each other and share NuGet packages (e.g. you are shipping a custom MVC project template with versions for Razor, Web Forms, C#, and VB.NET), we do not recommend adding the NuGet packages directly to each project template zip file. It needlessly increases the size of the project template bundle.

1. To specify the project template as a package repository you modify the <package>element:

   <packages repository="template">
       ...
   </packages>

The repository attribute now has the value “template” and the repositoryId attribute is not longer required. The nupkg files need to be placed into the root directory of the project template.

Database access is usually the largest performance bottleneck of web applications. But once you’ve optimized and cached your database queries as much as possible here are 3 quick tips that might help you squeeze out a few more requests out of your ASP.NET MVC applications and web servers.

Depending on which features you are using they might not always apply to your application and their benefit will not be that significant (a few % points improvement at most - sorry I don't have more specific numbers as I'm writing this from memory). I can't guarantee how much improvement you will see as it depends so much on what your application does. But I hope this will provide some leads for you to investigate. Just remember to always measure for your specific scenario.

Disable unused view engines

When: Your application is using built-in display/editor templates (via the Html.EditorFor or Html.DisplayFor methods) and you are using only one type of view engine.

Why: ASP.NET MVC is generally very good about caching file lookup hits (views, partials, display/editor templates). However one scenario that is not cached is the use of the built-in (default) display/editor templates (where all file lookups are misses).

Any time you use the Html.EditorFor or Html.DisplayFor methods and you do not have a matching template file MVC will generate the appropriate markup for you based on the model’s metadata. However, before that happens it checks all the view engines to find a template file. The more view engines you have registered the longer this will take and since the miss is not cached the process will have to be repeated the next time a page is requested. If you are using only one view engine in your project you should remove the other ones in Global.asax. The easies way to do that is with the following code:

ViewEngines.Engines.Clear();
ViewEngines.Engines.Add(new RazorViewEngine());

Avoid passing null models to views

When: You pass in a null model to a view that uses strongly-typed html helpers (such as Html.TextBoxFor). This frequently happens in Insert scenarios.

Why: Strongly-typed html helpers such as Html.TextBoxFor(m => m.Name) will try to emit the value of the model using the provided expression. However when something along the expression chain is null a NullReferenceException will be thrown when the expression gets evaluated. MVC’s expression evaluator catches the exception but on a page with multiple such html helpers the cost of the exception adds up. You can avoid that cost by always passing an instance of the model to the view:

public ActionResult Insert() {
    // return View(); // here the model instance defaults to null
    return View(new Product());
}

Uninstall URL Rewrite if you don’t use it

When: Your IIS server has the URL Rewrite module installed but none of the applications on the server are using it and you are running ASP.NET MVC 3.

Why: When performing URL generation (for example via a method like Html.ActionLink) in some cases MVC checks to see if the currently requested URL has been rewritten by the URL Rewrite module. If that is the case the result is processed so that it correctly matches the URL requested by the client.

The act of checking if a URL has been rewritten has a non-trivial cost (because it involves checking server variables). ASP.NET MVC 3 checks to see if URL Rewrite is turned off and can cache that fact thus avoiding the need to inspect server variables for each request. If URL Rewrite is turned on MVC will have to check server variables even if no rewriting happened for a particular request so if you are not using URL Rewrite you should turn it off (Note that MVC 2 always performs this check so turning URL Rewrite off will not make a difference).

Now that the final version of MVC 3 has been released I think information about the performance characteristics of this latest installment would be very useful for those weighing the pros and cons of updating their MVC 2 applications. In this post I will talk about what you might expect when moving to MVC 3. The short answer is things should be about the same.

Of course that short statement is not accurate because the only correct answer to such performance questions is: “it depends”. It depends on what your application does and which features it is using: database connections, business logic, output caching, html helpers, etc. I say this because in a moment I will present some numbers and they might not correspond to what you would see in your application. But they should provide you with a good starting point.

The more detailed answer is that some applications will perform better while others will perform worse. That is because as we added new features (dependency injection, improved filters, etc.) some components of MVC 3 got slower than in MVC 2 simply because they are now doing more work. At the same time we have introduced targeted performance optimizations which improved other components. The only definite way you can know the impact on your application is if you carefully measure performance yourself. At the end of this post I will provide a rough list of some of the things that have gotten faster or slower.

The Setup

The application I will use for the tests is the default “Internet Application” project template that ships with every installation of MVC. While quite small, it is still a pretty good choice because it uses a wide variety of MVC features. This means that the test exercises a large part of the framework without focusing on any individual features.

For my tests I have the following applications:

1. MVC 2 Aspx Internet Application project running against MVC 2 runtime
2. MVC 2 Aspx Internet Application project running against MVC 3 runtime
3. MVC 3 Aspx Internet Application project running against MVC 3 runtime
4. MVC 3 Razor Internet Application project running against MVC 3 runtime

I modified each of these applications in the following ways to ensure consistency and remove unnecessary noise from the results:

• Set debug=”false” in the root Web.config file.
• Changed application to build in Release mode.
• Changed the FormsAuthenticationService and MembershipService classes to return hardcoded values (I do not want to test database connection latency).

For each of the applications I executed the following sequence of requests and recorded the throughput (number of requests per second). The sequence ran for about 1 hour in our performance testing lab (meaning that the results should be amortized with respect to any other OS tasks that might have occurred on the server).

1. GET /Home/Index (arrive at site)
2. GET /Account/LogOn (click on “log on” link)
3. POST /Account/LogOn (attempt to log on with invalid credentials)
4. GET /Account/Register (click on “register” link)
5. POST /Account/Register (submit the registration form)

The Results

Note: The above results were captured on a 12-core server and should only be used for comparative purposes. Absolute RPS values on your own machine might de vastly different but their relative distribution should remain the same. 

Applications 1 vs. 2

As you can see from comparing the results for Application 1 and Application 2 the difference is quite small. In fact –1.82% falls within the margin of error. Application 1 and Application 2 are the same identical application, except 1. references System.Web.Mvc.dll version 2.0 and 2. references System.Web.Mvc.dll version 3.0. These results are why we say that MVC 3 is on par with the performance characteristics of MVC 2.

Of course followers of Scott Guthrie will point out that with the RC2 release he claimed that MVC 3 was faster than MVC 2. While that was true at the time it is not correct any longer for RTM. We had to undo a pretty significant performance fix related to model metadata caching because it caused some functional bugs (after all it does not matter how fast your application is if it does not actually work correctly). However, we will have that improvement available as an add-on in MVC Futures and we will roll it into MVC 4.

Applications 2 vs. 3

Comparing Application 2 with Application 3 shows that 3. is –6.64% slower. However, in this case the runtimes are the same. The difference is in the project templates used. The project template that ships with MVC 3 has more functionality enabled by default. Most notably it has unobtrusive client-side validation enabled; MVC 2 project templates did not have client-side validation enabled. The extra time is taken up inspecting the model metadata and emitting additional markup and javascript code. Of course while page rendering will be slower, the overall result of enabling client-side validation should be reduced load on the server as the majority of invalid inputs will be caught on the client thus avoiding the need for unnecessary roundtrips.

Applications 3 vs. 4

The comparison of Application 3 and Application 4 will be of interest to those looking at adopting the new Razor view engine. Application 4 is –4.3% slower than Application 3. This shows that using Razor does have a performance cost. However, that difference is not that big and is outweighed by the elegance and increased readability of the new view engine. Razor is also a new technology and I am sure that as it matures we will be able to optimize it even further.

The Changes

At the beginning of this post I promised that I would list how the various features or components of MVC changed in their performance characteristics. This list is compiled from our internal performance tests as well as change logs. It is meant to be taken as informational only. Your results may vary and depends on how you actually use each feature and what else you have happening in your application

Things that got faster (in no particular order):

• Expression caching (internal subsystem that helps in the performance of methods that accept lambdas)
• URL generation
• Action lookup
• Filter invocation
• TagBuilder

Things that got slower (also in no particular order):

• Things for which Dependency Injection entry points have been exposed
• Auto-generated editor and display helpers
• Model binding

Of course I am not going to tell you by how much things have changed because it depends... you will have to measure yourself.

We have just released the final version of ASP.NET MVC 3. Read the official MVC 3 release information or download MVC 3.

To help you upgrade your MVC 2 projects to MVC 3 we have released an upgrade tool. You can download it here: http://aspnet.codeplex.com/releases/view/59008. (This is an update of the tool that Eilon Lipton previously previewed on his blog and now we are giving it a more permanent home on our CodePlex site).

April 11 Update: We made a small update to the tool that allows you to skip the backup step. You might want to consider skipping the backup step if you use source control or if your solution is very big.

January 14 Update: We have updated the file on codeplex to fix an issue with converting solutions that had Web Sites or other solution items. If you are having problems please make sure you download the tool again from the codeplex site.

The upgrade tool only supports Visual Studio 2010 projects targeting .NET 4. Upgrading both MVC 2 and MVC 3 Beta (or RC) projects is supported.

The tool does not support Visual Studio 2008 solutions, MVC 1 projects, or projects targeting .NET 3.5. Those projects will first have to be upgraded using Visual Studio 2010 and/or retargeted for .NET 4:

• If you have a Visual Studio 2008 solution you can simply open it with Visual Studio 2010 to initiate the solution upgrade process.
• If your projects are targetting .NET 3.5 read how to target .NET 4.
• If you have a MVC 1.0 project you can use the old version of this tool to convert it to MVC 2.

The usage of the tool is quite simple:

1. If you use a source control system make sure your files are checked out and writable
2. Run the executable
3. Select your Visual Studio 2010 solution file that contains your project
4. Review the changes for each item in the Item details pane
5. Click on the Convert button to initiate the conversion process
6. Review the results in the Conversion log pane

During the conversion process the tool will:

1. Create a backup of the entire solution.
2. Update all class library projects (including Test projects) that reference System.Web.Mvc.dll to reference version 3.0.
3. Update all Web Application projects that reference System.Web.Mvc to reference version 3.0 and add references to System.Web.Helpers.dll and System.Web.WebPages.dll.
4. Change all MVC 2 Web Application projects to be MVC 3 projects (this affects which version of the 'Add View' dialog you get etc) 
5. Update all MVC Web Application root Web.config files:
   1. Update references to System.Web.Mvc version 3.0.
   2. Add an assembly binding redirect entry for System.Web.Mvc.
   3. Add assembly and namespace references to System.Web.Helpers and System.Web.WebPages.
   4. Add the “ClientValidationEnabled” and “UnobtrusiveJavaScriptEnabled” settings to the <appSettings> element with value “false” if they were not already present (these settings can be used to control the unobtrusive client validation and unobtrusive Ajax features).
6. Update all MVC Web Application views Web.config files (~\Views\Web.config as well as the views Web.config files for all Areas):
   1. Update references to System.Web.Mvc version 3.0
   2. Add a <configSections> entry required for Razor configuration in MVC
   3. Add the <system.web.webPages.razor> entry required for Razor support in MVC
   4. Add the “webPages:enabled” setting to the <appSettings> element with value “false” (required to prevent .cshtml or .vbhtml files in the Views folder from being directly accessible from a web browser)
7. Add the following JavaScript libraries to the MVC Web Applications (only if they did not already exist):
   • jQuery 1.4.4 (jquery-1.4.4.js, jquery-1.4.4-vsdoc.js, jquery-1.4.4.min.js)
   • jQuery UI 1.8.7 (jquery-ui.js, jquery-ui.min.js)
   • jQuery Validation 1.7 (jquery-validate.js, jquery-validate-vsdoc.js, jquery-validate.min.js)
   • Microsoft Ajax (MicrosoftAjax.js, Microsoft.Ajax.debug.js)
8. Overwrite MVC-specific JavaScript files in MVC Web Applications:
   • MicrosoftMvcAjax.js, MicrosoftMvcAjax.debug.js, MicrosoftMvcValidation.js, MicrosoftMvcValidation.debug.js, jquery.unobtrusive-ajax.js, jquery.unobtrusive-ajax.min.js, jquery.validate.unobtrusive.js, jquery.validate.unobtrusive.min.js
9. Add jQuery UI theme files (stylesheet and images)

This is an unsupported utility and there is a possibility that it might not work correctly for your solution. Specifically, the tool has the following limitations:

• Read-only project files are not supported (make sure you check out your solution if you use source control)
• Very long file paths might cause problems
• Solutions with project files outside of the solution folder might cause problems
• The tool will not upgrade your application code to account for any potential runtime breaking changes
• Non-standard project files (e.g. missing MVC project type GUID) will not be handled correctly
• Once again, VS 2008 solutions, MVC 1 or .NET 3.5 projects are not supported
• The tool will also not modify any Web Sites in your solution

However, if you run into problems let me know and I will see if we can get them addressed.