Things to check when you you experience high memory levels in ASP.NET
What is considered high memory?Obviously, this is going to be dependent on volume and activity of specific applications. But, in general, high memory is when see that your Aspnet_wp.exe process (Internet Information Services (IIS) 5.0) or W3wp process (IIS 6.0) memory is consistently increasing and is not returning to a comfortable level. In very general terms, a comfortable level would be under 600 MB in the default 2 GB user memory address space. Once the memory level is higher than that, we are performing less than we should be, and this may affect other applications running on the system. The key here is to understand that some applications require more memory than others, and if you are exceeding these limits, you may want to add more memory or add another server to your Web farm (or consider a Web farm). Also, profiling is recommended in these cases, which can enable developers to create leaner applications. In this article, we are looking at a situation where you consistently see memory rise until the server stops performing.
Common reasons for high memory
Application set up for debuggingOne reason for high memory that we see here in Support a lot is when you have debugging, tracing, or both enabled for your application. While you are developing your application, this is a necessity. By default, when you create your application in Visual Studio .NET, you will see the following attribute set in your Web.config file:
If you get nothing else from this article, I do hope you get this. Leaving debugging enabled is bad. We see this all too often, and it is so easy to change. Also, remember that this can be set at the page level, so make sure that all of your pages are not setting this.
String concatenationThere are applications that build HTML output by using server-side code and by just building one big HTML string to send to the browser. This is fine, but if you are building the string by using "+" and "&" concatenation, you may not be aware of how many large strings you are building. For example:
string mystring = "<html>";
mystring = mystring + "<table><tr><td>";
mystring = mystring + "First Cell";
mystring = mystring + "</td></tr></table>";
mystring = mystring + "</html>";
.NET Framework 1.1 Service Pack 1 (SP1)If you are not running the .NET Framework 1.1 SP1 yet, install this if you are experiencing memory issues. I won't go into great detail, but basically, with SP1 we are now allocating memory in a much more efficient manner. Basically, we are allocating 16 MB at a time for large objects rather than 64 MB at a time. We've all moved, and we all know that we can pack a lot more into a car or truck if we are using a lot of small boxes rather than a few large boxes. That is the idea here.
Don't be afraid to recycle periodicallyIn IIS 6.0, by default, we recycle application pools every 29 hours. In IIS 5.0, the Aspnet_wp.exe process will keep going until you end the task, restart IIS, or restart the computer. This means that this process could be running for months. For some applications, it's a pretty good idea to just restart the worker process every couple of days or so, at a convenient time.
Questions to askThe previous were all things that you can "fix" quickly. However, if you are experiencing memory issues, ask yourself these questions:
- Am I using a lot of large objects? More than 85,000 KB are stored in a large object heap.
- Am I storing objects in Session state? These objects are going to stay in memory for much longer than if you use and dispose them.
- Am I using the Cache object? When it is used wisely, this is a great benefit to performance. But when it is used unwisely, you wind up with a lot of memory used that is never released.
- Am I returning recordsets too large for a Web application? No one wants to look at 1,000 records on a Web page. You should be designing your application so that you never get more than 50 to 100 records in one trip.
DebuggingI won't get into setting up WinDbg. But here are some commands you can use to see what exactly is in your memory, if you wish to troubleshoot more complicated issues.
StringBuilder class, you will see a lot of System.String objects)
Once you have found an object taking a lot of memory, you can dig further by using the following command:
To learn more about how to set up and use these commands, take a look at this previous Support Voice column:
Garbage Collection: Automatic Memory Management in the Microsoft .NET Framework
Garbage Collection-Part 2: Automatic Memory Management in the Microsoft .NET Framework
Debugging Memory Problems
ASP.NET Performance Monitoring, and When to Alert Administrators
Improving .NET Application Performance and Scalability
10 Tips for Writing High-Performance Web Applications
Rediscover the Lost Art of Memory Optimization in Your Managed Code
Article ID: 893660 - Last Review: Jul 14, 2008 - Revision: 1