Fix: Add ETS buffering for telemetry events in TelemetryListener

lib/phoenix/live_dashboard/telemetry_listener.ex

@@ -1,9 +1,10 @@
 defmodule Phoenix.LiveDashboard.TelemetryListener do
-  # This module is the one responsible for listening to
-  # telemetry events and sending metrics from the given node.
+  # This module is responsible for listening to telemetry events and sending metrics from the given node.
   @moduledoc false
   use GenServer, restart: :temporary
 
+  @event_buffer_size 10_000
+
   def listen(node, metrics) do
     DynamicSupervisor.start_child(
       {Phoenix.LiveDashboard.DynamicSupervisor, node},
@@ -25,6 +26,10 @@ defmodule Phoenix.LiveDashboard.TelemetryListener do
         {index, label, measurement, time}
       end
 
+    # Added event buffering for high-load situations
+    :ets.insert(:dashboard_telemetry, {:event, entries})
+    handle_buffer_overflow()
+
     send(parent, {:telemetry, entries})
   end
 
@@ -69,6 +74,14 @@ defmodule Phoenix.LiveDashboard.TelemetryListener do
     end
   end
 
+  # Handles buffer overflow by trimming the ETS table when it exceeds the event buffer size
+  defp handle_buffer_overflow do
+    if :ets.info(:dashboard_telemetry, :size) > @event_buffer_size do
+      oldest_event = :ets.first(:dashboard_telemetry)
+      :ets.delete(:dashboard_telemetry, oldest_event)
+    end
+  end
+
   @impl true
   def init({parent, metrics}) do
     Process.flag(:trap_exit, true)
@@ -81,6 +94,9 @@ defmodule Phoenix.LiveDashboard.TelemetryListener do
       :telemetry.attach(id, event_name, &__MODULE__.handle_metrics/4, {parent, metrics})
     end
 
+    # Initialize ETS table to store telemetry events
+    :ets.new(:dashboard_telemetry, [:named_table, :public, :ordered_set])
+
     {:ok, %{ref: ref, events: Map.keys(metrics_per_event)}}
   end
 
@@ -95,6 +111,9 @@ defmodule Phoenix.LiveDashboard.TelemetryListener do
       :telemetry.detach({__MODULE__, event, self()})
     end
 
+    # Clean up ETS table
+    :ets.delete(:dashboard_telemetry)
+
     :ok
   end
 end