Add database metrics to Prometheus endpoint

lib/music_library_web/telemetry.ex

@@ -110,7 +110,30 @@ defmodule MusicLibraryWeb.Telemetry do
       last_value("vm.memory.total", unit: {:byte, :megabyte}),
       last_value("vm.total_run_queue_lengths.total"),
       last_value("vm.total_run_queue_lengths.cpu"),
-      last_value("vm.total_run_queue_lengths.io")
+      last_value("vm.total_run_queue_lengths.io"),
+
+      # Database Metrics
+      last_value("music_library.repo.query.total_time",
+        unit: {:native, :millisecond},
+        description: "The sum of the other measurements"
+      ),
+      last_value("music_library.repo.query.decode_time",
+        unit: {:native, :millisecond},
+        description: "The time spent decoding the data received from the database"
+      ),
+      last_value("music_library.repo.query.query_time",
+        unit: {:native, :millisecond},
+        description: "The time spent executing the query"
+      ),
+      last_value("music_library.repo.query.queue_time",
+        unit: {:native, :millisecond},
+        description: "The time spent waiting for a database connection"
+      ),
+      last_value("music_library.repo.query.idle_time",
+        unit: {:native, :millisecond},
+        description:
+          "The time the connection spent waiting before being checked out for the query"
+      )
     ]
   end