code: def _prep_save(self):
          
          log.info("Preparing bulk save.")
          self.graph.update_bulk_saver(self.bulk_saver)
  
          log.info(
              "Dropped %d unused preconditions, %d are missing",
              sum(len(v) for v in self.summary["precondition_entries"].values()),
              len(self.summary["missing_preconditions"]),
          )
  
          log.info(
              "Dropped %d unused postconditions, %d are missing",
              sum(len(v) for v in self.summary["postcondition_entries"].values()),
              len(self.summary["missing_postconditions"]),
          )
          del self.summary["postcondition_entries"]
docs: Prepares the bulk saver to load the trace graph info into the
          database.