FEATURE: if site is under extreme load show anon view

If a particular path is being hit extremely hard by logged on users,
revert to anonymous cached view.

This will only come into effect if 3 requests queue for longer than 2 seconds
on a *single* path.

This can happen if a URL is shared with the entire forum base and everyone
is logged on

lib/rate_limiter.rb

@@ -80,14 +80,17 @@ class RateLimiter
     PERFORM_LUA_SHA = Digest::SHA1.hexdigest(PERFORM_LUA)
   end
 
-  def performed!
+  def performed!(raise_error: true)
     return if rate_unlimited?
     now = Time.now.to_i
 
     if ((max || 0) <= 0) ||
        (eval_lua(PERFORM_LUA, PERFORM_LUA_SHA, [prefixed_key], [now, @secs, @max]) == 0)
 
-      raise RateLimiter::LimitExceeded.new(seconds_to_wait, @type)
+      raise RateLimiter::LimitExceeded.new(seconds_to_wait, @type) if raise_error
+      false
+    else
+      true
     end
   rescue Redis::CommandError => e
     if e.message =~ /READONLY/