GeoIP Service - Does It Use Lots of Resources

I was considering installing the PHP GeoIP Service onto my primary web server. This service will likely get about 400K requests per day (as I attempt to find the country location of each visitor).

My question is, this the best way to go about it? Will the resource usage doing it this way sink the web server (which is already under some duress)? Any other options you recommend?

I’m doing it to decide if a person is in Canada and, if they are, give them a separate Ad Tag.

All feedback appreciated!

Should be fairly light resource usage…Essentially, what geoIP does is download a massive CSV file containing IP range -> country pairings every so often, and when you ask for geoip_country, it does a flat-file-database style equivalent of 'SELECT country WHERE startint <= ip AND endint >= ip (it stores both dotted notation and integer conversion forms of the IP range data)