Arnaud,

I believe what I have to do now is to build some solid queries to explore
our activity
log...

Unless I'm mistaken, I believe that you may have misread Richard's
advice.  (Correct me if I'm wrong, Richard.) His recommendation:

I stress accounting log reporting because it is the very best, detailed handle
on what your clients are throwing at the server

Accounting log records are comma-delimited records written to a flat file
called dsmaccnt.log, assuming that you have accounting turned on.  If you
don't, I would recommend that you turn it on now...

The accounting log records give a very detailed, session-by-session picture
of the activity between the server and clients. It will be easier to parse
and process than what you can get out of the activity log.

Ted