Are you aware of any serious performance problems with checking if a file exists before you open it and send it? The context for this is a web application that serves up files dynamically via an ASP page. I was told that there is no check for whether or not the file exists because the database stores this information and shouldn’t be wrong. It is of course sometimes wrong for any number of reasons so we end up sending back nothing leaving the user unhappy.
My instinct is that checking for a file’s existence is so cheap that you shouldn’t worry about it but I was told otherwise. Our storage solution is a pretty high powered one (not just an IDE drive on the web server) if that helps. My question is basically: Is my instinct correct?
Thanks!
Note: These files are never just deleted. Something has to go wrong for them to be missing but this happens a few times a week. Also, the reason I want to check for a file’s existence is because I can return an alternate asset that is on disk so I’d like to be able to have that logic all in one spot rather than deal with catching an exception and dealing with that in that context.
Even if you check it exists just before you try to serve it, it could be deleted between the check and you serving it.
The problem here is that you send back nothing if you can’t serve the file. Trying to serve a non-existent file should throw an exception (or whatever the equivalent is on your platform) – you should handle that exception by returning an appropriate ‘Sorry, we couldn’t find your file’ error page.