File downloads

Dear All, I have a HTTP server + MySQL database. Everytime a file is requested for download, my PHP script loads the content from the database into a temporary file (on the server). I then pass a URL to the client, with a link to this file. The client can thus download the file at any time. However, I can foresee many problems with this approach. One is, when to delete the temporary file? Also with more than one client, this approach would have to be refined. Security is also an issue: One user may read another's files. Can anyone kindly give me an alternative approach? I reiterate, I cannot supply static URLs as the downloadable file is generated on-demand. Thanks & Regards KM