Originally posted on: http://geekswithblogs.net/Aligned/archive/2013/06/24/asp.net-4.5-garbage-collection-improvement.aspx

I just read Five Great .NET Framework 4.5 Features on CodeProject by Shivprasad koirala. Feature 5 in his article mentions the GC background cleanup and has a good explanation of the work the GC has to do for ASP.Net on the server. “Garbage collector is one real heavy task in a .NET application. And it becomes heavier when it is an ASP.NET application. ASP.NET applications run on the server and a lot of clients send requests to the server thus creating loads of objects, making the GC really work hard for cleaning up unwanted objects.”

“To overcome the above problem, server GC was introduced. In server GC there is one more thread created which runs in the background. This thread works in the background and keeps cleaning…objects thus minimizing the load on the main GC thread. Due to double GC threads running, the main application threads are less suspended, thus increasing application throughput. To enable server GC, we need to use the gcServer XML tag and enable it to true.”

<configuration>
   <runtime>
      <gcServer enabled="true"/>
   </runtime>
</configuration>

This is not done by default. The MSDN information page says “There are only two garbage collection options, workstation or server. For single-processor computers, the default workstation garbage collection should be the fastest option. Either workstation or server can be used for two-processor computers. Server garbage collection should be the fastest option for more than two processors. Use the GCSettingsIsServerGC property to determine if server garbage collection is enabled.”

“In the .NET Framework 4 and earlier versions, concurrent garbage collection is not available when server garbage collection is enabled. Starting with the .NET Framework 4.5, server garbage collection is concurrent. To use non-concurrent server garbage collection, set the <gcServer> element to true and the <gcConcurrent> element to false. “

So if you’re using ASP.Net 4.5 and have a multi-core server, you should try turning on the Server Garbage Collection and do some profiling to see if it improves the performance of your site.