From 221234945476fe6a33fc5ee57d3b8a7b64c25790 Mon Sep 17 00:00:00 2001
From: Max Wofford <max@maxwofford.com>
Date: Wed, 25 Jun 2025 20:20:07 -0400
Subject: [PATCH] Add rps tracker to footer (#364)

---
 app/controllers/application_controller.rb |  5 ++
 app/helpers/application_helper.rb         |  5 ++
 app/lib/request_counter.rb                | 57 +++++++++++++++++++++++
 app/views/layouts/application.html.erb    |  1 +
 4 files changed, 68 insertions(+)
 create mode 100644 app/lib/request_counter.rb

diff --git a/app/controllers/application_controller.rb b/app/controllers/application_controller.rb
index 2f42bd7..c10008e 100644
--- a/app/controllers/application_controller.rb
+++ b/app/controllers/application_controller.rb
@@ -3,6 +3,7 @@ class ApplicationController < ActionController::Base
   before_action :honeybadger_context, if: :current_user
   before_action :initialize_cache_counters
   before_action :try_rack_mini_profiler_enable
+  before_action :track_request
   after_action :track_action
 
   around_action :switch_time_zone, if: :current_user
@@ -30,6 +31,10 @@ class ApplicationController < ActionController::Base
     ahoy.track "Ran action", request.path_parameters
   end
 
+  def track_request
+    RequestCounter.increment
+  end
+
   def try_rack_mini_profiler_enable
     if current_user && current_user.is_admin?
       Rack::MiniProfiler.authorize_request
diff --git a/app/helpers/application_helper.rb b/app/helpers/application_helper.rb
index 6653306..b75902b 100644
--- a/app/helpers/application_helper.rb
+++ b/app/helpers/application_helper.rb
@@ -5,6 +5,11 @@ module ApplicationHelper
     { hits: hits, misses: misses }
   end
 
+  def requests_per_second
+    rps = RequestCounter.per_second
+    rps == :high_load ? "lots of req/sec" : "#{rps} req/sec"
+  end
+
   def admin_tool(class_name = "", element = "div", **options, &block)
     return unless current_user&.is_admin?
     concat content_tag(element, class: "admin-tool #{class_name}", **options, &block)
diff --git a/app/lib/request_counter.rb b/app/lib/request_counter.rb
new file mode 100644
index 0000000..b42934c
--- /dev/null
+++ b/app/lib/request_counter.rb
@@ -0,0 +1,57 @@
+class RequestCounter
+  WINDOW_SIZE = 10 # seconds - shorter window for more responsive rates
+  HIGH_LOAD_THRESHOLD = 500 # req/sec to disable tracking
+  CIRCUIT_BREAKER_DURATION = 30 # seconds to stay disabled
+
+  @buckets = {}
+  @disabled_until = nil
+
+  class << self
+    def increment
+      return if disabled?
+
+      current_time = Time.current.to_i
+      @buckets[current_time] = (@buckets[current_time] || 0) + 1
+
+      # Check if we should disable due to high load
+      check_circuit_breaker(current_time)
+
+      # Periodically clean old buckets (1% chance)
+      cleanup if rand(100) == 0
+    end
+
+    def per_second
+      return :high_load if disabled?
+
+      current_time = Time.current.to_i
+      cutoff = current_time - WINDOW_SIZE
+
+      total = @buckets.select { |timestamp, _| timestamp >= cutoff }.values.sum
+      (total.to_f / WINDOW_SIZE).round(2)
+    end
+
+    private
+
+    def disabled?
+      @disabled_until && Time.current.to_i < @disabled_until
+    end
+
+    def check_circuit_breaker(current_time)
+      # Check last 5 seconds for high load
+      recent_total = @buckets.select { |ts, _| ts >= current_time - 5 }.values.sum
+
+      if recent_total > HIGH_LOAD_THRESHOLD * 5 # 5 seconds worth
+        @disabled_until = current_time + CIRCUIT_BREAKER_DURATION
+        @buckets.clear # Clear to reduce memory
+      end
+    end
+
+    def cleanup
+      return if disabled? # Skip cleanup when disabled
+
+      current_time = Time.current.to_i
+      cutoff = current_time - WINDOW_SIZE - 10 # extra buffer
+      @buckets.reject! { |timestamp, _| timestamp < cutoff }
+    end
+  end
+end
diff --git a/app/views/layouts/application.html.erb b/app/views/layouts/application.html.erb
index 142e72d..cfb9cfe 100644
--- a/app/views/layouts/application.html.erb
+++ b/app/views/layouts/application.html.erb
@@ -168,6 +168,7 @@
             in the last 24 hours.
             (DB: <%= pluralize(QueryCount::Counter.counter, "query") %>, <%= QueryCount::Counter.counter_cache %> cached)
             (CACHE: <%= cache_stats[:hits] %> hits, <%= cache_stats[:misses] %> misses)
+            (<%= requests_per_second %>)
           </p>
           <% if session[:impersonater_user_id] %>
             <%= link_to "Stop impersonating", stop_impersonating_path, class: "impersonate-link", data: { turbo_prefetch: "false" } %>