How are .ascx files cached?

I have an asp.net project, and I load a base aspx page to display to the user. Then I ajax in the results of an ascx component and inject it via innerHTML in javascript.

I have noticed that the ascx component loads slowly on the first page load, but instantly thereafter. This is really cool, but I do not understand how this can be 开发者_JAVA百科cached, as the contents are generated by making several db calls.

Does the server send some kind of hash to compare the contents to, to see if it changed on the server or not? Is this a browser thing or an asp.net thing?

What you are experiencing is most likely just in time compiling and has very little to do with the user control itself.

Watch the performance monitor counters for .net. This will tell you a lot about what's going on.

Can you use Firebug/IE developer console/etc. to determine the response code? If you can check the headers, you should be able to see a date that indicates either a cache time or a last modified date. I poked through the MS ASP.NET Ajax documentation, but couldn't find any references to default caching times or cache modification.

However, jQuery's ajax function uses an ifModified property which (according to the documentation) checks the Last-Modified header to determine whether or not it should retrieve the results. I'd imagine that the ASP.NET Ajax calls work in a similar fashion. It may not be prudent for your current project, but jQuery makes it very easy to set caching options.