Attempt to sync request counter between processes

app/helpers/application_helper.rb

@@ -10,6 +10,11 @@ module ApplicationHelper
     rps == :high_load ? "lots of req/sec" : "#{rps} req/sec"
   end
 
+  def global_requests_per_second
+    rps = RequestCounter.global_per_second
+    rps == :high_load ? "lots of req/sec" : "#{rps} req/sec (global)"
+  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)

app/lib/request_counter.rb

@@ -2,9 +2,12 @@ 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
+  PROCESS_ID = "#{Socket.gethostname}-#{Process.pid}"
+  STATS_DIR = Rails.root.join("tmp", "request_stats")
 
   @buckets = {}
   @disabled_until = nil
+  @last_sync = 0
 
   class << self
     def increment
@@ -16,8 +19,11 @@ class RequestCounter
       # 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
+      # Periodically sync to file and cleanup (1% chance)
+      if rand(100) == 0
+        sync_to_file(current_time)
+        cleanup
+      end
     end
 
     def per_second
@@ -26,7 +32,36 @@ class RequestCounter
       current_time = Time.current.to_i
       cutoff = current_time - WINDOW_SIZE
 
-      total = @buckets.select { |timestamp, _| timestamp >= cutoff }.values.sum
+      # Fast local calculation
+      local_total = @buckets.select { |timestamp, _| timestamp >= cutoff }.values.sum
+      (local_total.to_f / WINDOW_SIZE).round(2)
+    end
+
+    def global_per_second
+      return :high_load if disabled?
+
+      current_time = Time.current.to_i
+      sync_to_file(current_time)
+
+      # Read and aggregate from all process files
+      cutoff = current_time - WINDOW_SIZE
+      total = 0
+
+      Dir.glob(STATS_DIR.join("*.txt")).each do |file_path|
+        next unless File.mtime(file_path) > (cutoff - 60).seconds.ago # Skip very old files
+
+        begin
+          File.read(file_path).each_line do |line|
+            next if line.strip.empty?
+            timestamp, count = line.strip.split(":", 2)
+            next unless timestamp && count
+            total += count.to_i if timestamp.to_i >= cutoff
+          end
+        rescue Errno::ENOENT
+          # Skip deleted files
+        end
+      end
+
       (total.to_f / WINDOW_SIZE).round(2)
     end
 
@@ -37,7 +72,7 @@ class RequestCounter
     end
 
     def check_circuit_breaker(current_time)
-      # Check last 5 seconds for high load
+      # Check last 5 seconds for high load (local only for performance)
       recent_total = @buckets.select { |ts, _| ts >= current_time - 5 }.values.sum
 
       if recent_total > HIGH_LOAD_THRESHOLD * 5 # 5 seconds worth
@@ -46,12 +81,40 @@ class RequestCounter
       end
     end
 
-    def cleanup
-      return if disabled? # Skip cleanup when disabled
+    def sync_to_file(current_time)
+      return if current_time == @last_sync || @buckets.empty?
 
+      ensure_stats_dir
+      file_path = STATS_DIR.join("#{PROCESS_ID}.txt")
+
+      # Atomic write: write to temp file then rename
+      temp_path = "#{file_path}.tmp"
+      data = @buckets.map { |timestamp, count| "#{timestamp}:#{count}" }.join("\n")
+      File.write(temp_path, data)
+      File.rename(temp_path, file_path)
+
+      @last_sync = current_time
+    rescue Errno::ENOENT, Errno::EACCES
+      # Silently fail if we can't write (e.g., read-only filesystem)
+    end
+
+    def ensure_stats_dir
+      FileUtils.mkdir_p(STATS_DIR) unless Dir.exist?(STATS_DIR)
+    end
+
+    def cleanup
       current_time = Time.current.to_i
       cutoff = current_time - WINDOW_SIZE - 10 # extra buffer
       @buckets.reject! { |timestamp, _| timestamp < cutoff }
+
+      # Clean up old process files (10% chance)
+      return unless rand(10) == 0
+
+      Dir.glob(STATS_DIR.join("*.txt")).each do |file_path|
+        File.delete(file_path) if File.mtime(file_path) < (cutoff - 60).seconds.ago
+      rescue Errno::ENOENT
+        # File already deleted
+      end
     end
   end
 end