It only shows up in the source a couple of times, but it's crucial. `middleware.py` inserts rows into it: <https://github.com/okfn/ckan/blob/master/ckan/config/middleware.py#L343> and `cli.py` pulls them out again: <https://github.com/okfn/ckan/pull/730/files#r3812857>. As users view pages, each view gets recorded in the `tracking_raw` table, then the `paster tracking update` command updates the `tracking_summary` table based on what's in `tracking_raw`.