ASMX Web Service slow first request

Question

I have a bunch of .NET Webservices running in one IIS Application. These webservices are consumed by another IIS Application (frontend). The first call is pretty slow, about 5 to 10 seconds. After that it’s just milliseconds. The first call is considered a performance problem.

We’ve tried an application that calls all these webservices but this obviously doesn’t solve anything. So it's not the default Application Recycle that is the problem. I've created an application that just initializes the service several times and measures the time it takes to create one instance. Before running this application I ensure that my webservice application is started / recycled, then I run the application. The first initialization takes between 2 to 4 seconds, all others is just milliseconds.

Another thought is that we create a page in the Frontend application that initiates all the webservices and that we call this page before any users are in. I don’t consider this as an elegant solution, what else could I try?

Answer 1

The delay that is experienced when a client is calling a webservice for the first time is caused by the fact that by default a XmlSerializers dll for the webservice needs to be compiled. This is causing the 2-4 seconds for the initial call. Of course this is the case when the webservice application is already running, if it's not you would have a recycle. In which case the other answers could help.

To speed up the initial call you can create the XmlSerializers dll at compile time. You can do this by setting your project build 'Generate serialization assembly' to on. This generates an MyApplication.XmlSerializers.dll containing the webservice information. Now the initial call dropped to 300 ms, presumably the loading of the dll. All calls there after take 0 ms.

In Visual Studio right click on your project and choose 'Properties'. Go to the 'Build' Tab. There you have an option 'Generate Serialization assembly' in the 'Output' section. If you change the value to 'On' the serialization assembly will be generated during compile time.

Answer 2

The first time you call the webservice, or the first time after a long delay, the web service needs to start up. This is where you're seeing the delay. After that, it's already started and will respond really quickly to calls. This is standard web service behaviour.

You could configure IIS to have keepalive = true - which may improve the performance.

More information as requested.

It could be that the serialization assemblies are being created at runtime. You can change the settings of the serialization assembly using the dropdown at the bottom of the Build pane of the properties window for the project.

It could be that you have written your web service to perform a lot of operations on application start, which would happen the first time a method on the service is called.

It might be that the operation is very slow, but you are then caching the response, which makes subsequent calls faster.