The rephist subsystem seems to track EXTEND cells attempt (on the client side) but the overall results of this is not used except in `rep_hist_dump_stats()`. This is the only use of `link_history_t` also afaict. See: ``` void rep_hist_note_extend_succeeded(const char *from_name, const char *to_name); void rep_hist_note_extend_failed(const char *from_name, const char *to_name); ``` Furthermore, tor tracks downtime and uptime of relays but actually never use that information anywhere. See: ``` void rep_hist_note_connect_failed(const char* nickname, time_t when); void rep_hist_note_connect_succeeded(const char* nickname, time_t when); void rep_hist_note_disconnect(const char* nickname, time_t when); void rep_hist_note_connection_died(const char* nickname, time_t when); ``` The side effect of this is that we keep adding objects to the `history_map` that are wasting memory and never used in the end except when we dump statistics. By removing this, we would cleanup quite a bit of code and effectively make the `or_history_t` object *ONLY* useful to directory authorities for relay reachability tracking.