If you use Apache version 2.X, I would recon you are using
mod_log_config to log request information to the access_log (if you
are not using mod_log_config, I assume you are a busy site that has
disable logging to boost performance). This is a nifty module, and after
reading the source (the source for mod_log_config is located in
SRCROOT/modules/loggers/mod_log_config.c I learned that this module`
has TONS of nifty options to control what gets logged. In addition to
logging request data and browser information, you can also log cookie
data, request processing time (this requires mod_status and
ExtendedStatus), HTTP headers, notes, IP addresses, ports, and numerous
other
options. If
you are using logfile analysis utilities that require Custom/Combined
formatted access_logs, you need to be careful where you add these
options to avoid breaking your reporting tools. Apache is swell!