relay: Don't make DNS timeout trigger an overload

Tor has configure libevent to attempt up to 3 times a DNS query for a
maximum of 5 seconds each. Once that 5 seconds has elapsed, it consider
the query "Timed Out" but tor only gets a timeout if all 3 attempts have
failed.

For example, using Unbound, it has a much higher threshold of timeout.
It is well defined in
https://www.nlnetlabs.nl/documentation/unbound/info-timeout/ and has
some complexity to it. But the gist is that if it times out, it will be
much more than 5 seconds.

And so the Tor DNS timeouts are more of a "UX issue" rather than a
"network issue". For this reason, we are removing this metric from the
overload general signal.

See https://gitlab.torproject.org/tpo/network-health/team/-/issues/139
for more information.

Fixes #40527

Signed-off-by: David Goulet <dgoulet@torproject.org>

1 files changed, 0 insertions, 12 deletions

diff --git a/src/feature/stats/rephist.c b/src/feature/stats/rephist.c
index c3a281a8c2..2bfa14d326 100644
--- a/src/feature/stats/rephist.c
+++ b/src/feature/stats/rephist.c
@@ -283,18 +283,6 @@ overload_general_dns_assessment(void)
     return;
   }
 
-  /* Lets see if we can signal a general overload. */
-  double fraction = (double) overload_dns_stats.stats_n_error_timeout /
-                    (double) overload_dns_stats.stats_n_request;
-  if (fraction >= overload_dns_timeout_fraction) {
-    log_notice(LD_HIST, "General overload -> DNS timeouts (%" PRIu64 ") "
-               "fraction %.4f%% is above threshold of %.4f%%",
-               overload_dns_stats.stats_n_error_timeout,
-               fraction * 100.0,
-               overload_dns_timeout_fraction * 100.0);
-    rep_hist_note_overload(OVERLOAD_GENERAL);
-  }
-
  reset:
   /* Reset counters for the next period. */
   overload_dns_stats.stats_n_error_timeout = 0;