2 files changed, 34 insertions(+), 0 deletions(-)

M lib/triglav/application.ex
A lib/triglav/telemetry.ex

@@ 19,6 19,8 @@ defmodule Triglav.Application do
         ]
       end
 
+    Triglav.Telemetry.start!()
+
     opts = [strategy: :one_for_one, name: Triglav.Supervisor]
     Supervisor.start_link(children, opts)
   end

@@ 0,0 1,32 @@
+defmodule Triglav.Telemetry do
+  require Logger
+
+  @slow_query_threshold_ms 500
+
+  def start! do
+    :ok = :telemetry.attach("triglav", [:triglav, :repo, :query], &Triglav.Telemetry.handle_event/4, %{})
+  end
+
+  def handle_event([:triglav, :repo, :query], measurements, metadata, _config) do
+    if ms(measurements.total_time) > @slow_query_threshold_ms do
+      timings = measurements
+      |> Map.take([:total_time, :query_time, :idle_time])
+      |> Map.new(fn {k, v} -> {k, ms(v)} end)
+
+      log_message = """
+      SLOW QUERY ( > #{@slow_query_threshold_ms}ms ) #{inspect(timings)}
+        query: #{metadata[:query]}
+        params: #{inspect(metadata[:params])}
+      """
+
+      Logger.warning(log_message)
+    end
+  end
+
+  def handle_event(_, _, _, _) do
+    :ok
+  end
+
+  defp ms(nil), do: nil
+  defp ms(native), do: :erlang.convert_time_unit(native, :native, :millisecond)
+end