Which hook to use in a custom module for tracking access to one particular page?
That's how I achieved that:

function grap_contact_export_csv_page() {
  grap_log_export(); // Calling another function to record tracking in DB
  header("Cache-Control: public");
  header("Content-Type: application/octet-stream");
  header("Cache-Control: no-store, no-cache, must-revalidate");
  header("Cache-Control: post-check=0, pre-check=0");
  header("Content-Disposition: attachment; filename=\"grape-export.csv\";" );
  header("Content-Transfer-Encoding: binary");
  $fp = fopen('export.csv', 'r') or die('Impossible d\'accéder au fichier');
  echo fread($fp, filesize('export.csv'));
  fclose($fp);
  drupal_exit();
}