Thanks, Allen, I might try that.
But what I really need is to be able to measure the total traffic.
I wrote a simple Perl script which analyzes the access logs and produces daily, weekly and monthly totals and averages. But I don't know whether these stats reflect the compressed or uncompressed sizes.
I know that mod_gzip allows you to add the compressed size, uncompressed size and compression ratio to the access log. Maybe I should use that instead of zlib. It would probably be better anyway, since it would compress pages served from outside the scripts.
Server resource utilization shouldn't be an issue, since it's a dedicated server, but we have bandwidth contraints, so compression is a priority.
