This post was most recently updated on October 4th, 2022.

2 min read.

This post describes one of the more no-brainerish ways of fixing a ‘System.OutOfMemoryException’ exception being thrown in your ASP.Net MVC application using C# and Entity Framework.

Problem

Table of Contents

While developing a web project, for example, an ASP.NET MVC web application that is using EF, sometimes when handling a lot of data or complex entities on your dev machine, you encounter this error:

OutOfMemoryException: Exception of type 'System.OutOfMemoryException' was thrown.]
   System.Text.StringBuilder.ToString() +35
   System.IO.StreamReader.ReadToEnd() +123
   System.Web.Optimization.BundleFile.ApplyTransforms() +74
   System.Web.Optimization.DefaultBundleBuilder.BuildBundleContent(Bundle bundle, BundleContext context, IEnumerable`1 files) +472
   System.Web.Optimization.Bundle.GenerateBundleResponse(BundleContext context) +127
   System.Web.Optimization.Bundle.GetBundleResponse(BundleContext context) +45
   System.Web.Optimization.BundleResolver.GetBundleContents(String virtualPath) +166
   System.Web.Optimization.AssetManager.DeterminePathsToRender(IEnumerable`1 assets) +205
   System.Web.Optimization.AssetManager.RenderExplicit(String tagFormat, String[] paths) +35
   System.Web.Optimization.Scripts.RenderFormat(String tagFormat, String[] paths) +107
   System.Web.Optimization.Scripts.Render(String[] paths) +21

This of course blocks you from debugging or even running at least this part of your code locally. What to do?

Reason

By default, Visual Studio uses a 32-bit version of IIS Express for your deployments. A lot of times, this is good and intended, and not a problem. In some rare cases, this might mean, however, that your IIS processes are running out of memory.

I’m going to argue, that most of the time you shouldn’t end up having this issue if your code is sane and smart. Most of the time, if you get this error, you’re building infinite loops or forcing the Entity Framework to load millions and millions of rows in memory. Fix that first.

However, with EF it’s somewhat easy to build apps that use a lot of memory, but work as they should. Perhaps your architecture does make sense, and using a lot of memory is ok?

In this case, you might want to accommodate this memory requirement by enabling a 64-bit version of IIS locally. That’s probably what you’re using in production anyway.

This is luckily a pretty easy change.

How to solve System.OutOfMemoryException in Visual Studio?

The first thing is to make sure you’re not hogging all the available memory for no reason – no neverending loops or infinite recursion! After that, consider the following.

Time needed: 5 minutes

How to enable 64-bit IIS Express from Visual Studio settings

Navigate to the following settings page:
Visual Studio > Tools > Options > Projects and Solutions > Web Projects
Enable the following setting
“Use the 64-bit version of IIS Express for websites and projects” (see screenshot 1 below)

Screenshot 1: How to enable the 64-bit version of IIS Express in Visual Studio 2017
Also, don’t forget to verify you’re building a 64-bit version of your app!
See screenshot 2 below:

Screenshot 2: 64-bit build option for the solution in Visual Studio

And you should be good to go!

Author
Recent Posts

Antti K. Koskela

Developer / Speaker / Consultant at Koskila / Precio Fishbone / Norppandalotti Software Co / Alter - Experience Ideas Ltd

Antti Koskela is a proud digital native nomadic millennial full stack developer (is that enough funny buzzwords? That's definitely enough funny buzzwords!), who works as Solutions Architect for Precio Fishbone, building delightful Digital Workplaces.

He's been a developer from 2004 (starting with PHP and Java), and he's been working on .NET projects, Azure, Office 365, SharePoint and a lot of other stuff. He's also Microsoft MVP for Azure.

This is his personal professional (e.g. professional, but definitely personal) blog.

Latest posts by Antti K. Koskela (see all)