Is there a way to get PHP to release this file?

I am editing a data file via ODBC, and would like to be able to download the updated file in the same transaction when finished. It seems, however, that even after calling odbc_close(), PHP still retains a lock on the file for the duration of the request. Is there a way to get PHP to release the file? (Ideally, I'd prefer to work in memory and/or streams altogether rather than saving the changes to a file, but I'm not sure that's possible with odbc_connect.) I guess if I have to I can issue a redirect to a second process that would download the file, but I'd prefer having to pass a one-time URL to the browser where it will end up in the history. Andrew