ASP.NET: are aspx/ascx files accessed from disk on every request?

I googled forever, and I couldn't find an answer to this; the answer is either obvious (and I need more training) or it's buried deep in documentation (or not documented). Somebody must know this.

I've been arguing with somebody who insisted on caching some static files on an ASP.NET site, where I thought it's not necessary for a simple fact that all other files that produce dynamic HTML are not cached (by default; let's ignore output caching for now; let's also ignore the caching mechanism that person had in mind [in-memory or out on network]). In other words, why cache some xml file (regardless on how frequently开发者_如何学运维 it's accessed) when all aspx files are read from disk on every request that map to them? If I'm right, by caching such static files very little would be gained (less disk-read operations), but more memory would be spent (if cached in memory) or more network operations would be caused (if cached on external machine). Does somebody know what in fact happens when an aspx file is [normally] requested? Thank you.

If I'm not mistaken ASPX files are compiled at run-time, on first access. After the page is compiled into an in-memory instance of a Page class, requests to the same resource (ASPX page) are serviced against the object in memory. So in essence, they are cached with respect to disk-access.

Obviously the dynamic content is generated for every request, unless otherwise cached using output caching mechanisms.

Regarding memory consumption vs disk access time, I have to say that from the performance stand point it makes sense to store objects in memory rather than reading them from disk every time if they are used often. Disk access is 2 orders of magnitude slower than access in RAM. Although inappropriate caching strategies could push frequently used objects out of memory to make room for seldom used objects which could hurt performance for obvious reasons. That being said, caching is really important for a high-performance website or web application.

As an update, consider this:

• Typical DRAM access times are between 50 - 200 nano-seconds
• Average disk-access times are in the range of 10 - 20 milliseconds

That means that without caching a hit against disk will be ~200 times slower than accessing RAM. Of course, the operating system, the hard-drive and possible other components in between may do some caching of their own so the slow-down may only occur on first hit if you only have a couple such files you're reading from.

Finally, the only way to be certain is to do some benchmarking. Stress-test both implementations and choose the version that works best in your case!

IIS does a large amount of caching, so directly, no. But, IIS checks for ANY changes in the web directory and reloads any changed files as they get changed. Sometimes IIS gets borked and you have to restart it to detect changes, but usually it works pretty good.

P.S. The caching mechanisms may flush data frequently based on server usage, but the caching works for all files in the web directory. Any detected changes to source code causes IIS to flush the web applicaiton and re-compile/re-load as well.

I believe that the answer to your question depends on both the version of IIS you're using, and configuration settings.

But I believe that it's possible to configure some combinations of IIS/.Net to avoid checking the files - there's an option to pre-compile sites, so no code actually needs to be deployed to the web server.