A visit is either NEW or KNOWN.
- If a visit is NEW then we process the visitor information (settings, referrers, etc.) and save
a new line in the log_visit table.
- If a visit is KNOWN then we update the visit row in the log_visit table, updating the number of pages
views, time spent, etc.
Whether a visit is NEW or KNOWN we also save the action in the DB.
One request to the piwik.php script is associated to one action.