Maximum server file access frequency

Question

I'm trying to create a AJAX push implementation in PHP using a Comet long-polling method. My code involves using file_get_contents() to read a file repeatedly to check for any messages to send to the user. To reduce server load, I'm using two text files; one containing the actual command and one acting as a "change notifier", which either is iterated through 0-9 or contains a UNIX timestamp. My question is, how often can I access and read from a small (only a few bytes) file without overloading the server? The push implementation means that I can poll for changes much more often than requesting a file every few seconds, but there's still must be a limit.

If it helps, I'm using the 1&1 Home (Linux) hosting plan, which is shared hosting.

Answer 1

Assuming you're running a sane os which will cache the 'change notifier' file in ram, the operation would be so cheap as to insignificant. PHP would become a bottleneck way before then.