chore: add cache health logging (#601)

Author: KaylaBrady

config/config.exs

@@ -30,11 +30,14 @@ config :mobile_app_backend, alerts_with_summaries_broadcast_interval_ms: 60_000
 config :mobile_app_backend, predictions_broadcast_interval_ms: 5_000
 config :mobile_app_backend, vehicles_broadcast_interval_ms: 500
 
-config :mobile_app_backend, MBTAV3API.ResponseCache, allocated_memory: 250_000_000
+config :mobile_app_backend, MBTAV3API.ResponseCache,
+  allocated_memory: 250_000_000,
+  stats: true
 
 config :mobile_app_backend, MBTAV3API.RepositoryCache,
   gc_interval: :timer.hours(2),
-  allocated_memory: 2_000_000_000
+  allocated_memory: 2_000_000_000,
+  stats: true
 
 config :mobile_app_backend, MobileAppBackend.Search.Algolia.Cache,
   gc_interval: :timer.hours(6),

lib/mobile_app_backend/application.ex

@@ -36,7 +36,16 @@ defmodule MobileAppBackend.Application do
         {Ecto.Migrator, repos: Application.fetch_env!(:mobile_app_backend, :ecto_repos)},
         {Oban, Application.fetch_env!(:mobile_app_backend, Oban)},
         {MobileAppBackend.Search.Algolia.Cache, []},
-        {MobileAppBackend.Health.Cache, cache: MobileAppBackend.Search.Algolia.Cache},
+        Supervisor.child_spec(
+          {MobileAppBackend.Health.Cache, cache: MobileAppBackend.Search.Algolia.Cache},
+          id: :search_cache_stats
+        ),
+        Supervisor.child_spec({MobileAppBackend.Health.Cache, cache: MBTAV3API.RepositoryCache},
+          id: :repo_cache_stats
+        ),
+        Supervisor.child_spec({MobileAppBackend.Health.Cache, cache: MBTAV3API.ResponseCache},
+          id: :response_cache_stats
+        ),
         MobileAppBackend.MapboxTokenRotator,
         MobileAppBackend.Alerts.Registry,
         MobileAppBackend.Predictions.Registry,

lib/mobile_app_backend/health/cache.ex

@@ -22,9 +22,9 @@ defmodule MobileAppBackend.Health.Cache do
       nil ->
         Logger.info("#{__MODULE__} cache=#{cache} cache stats disabled")
 
-      {:ok, %{stats: %{hits: cache_hits, misses: cache_misses}}} ->
+      {:ok, %{stats: stats}} ->
         Logger.info(
-          "#{__MODULE__} cache=#{cache} cache_health hits=#{cache_hits} misses=#{cache_misses} hit_rate=#{cache_hits / max(cache_hits + cache_misses, 1)}"
+          "#{__MODULE__} cache=#{cache} cache_health #{Enum.map_join(stats, " ", fn {key, val} -> "#{key}=#{val}" end)}}"
         )
 
       {:error, error} ->

test/mobile_app_backend/health/cache_test.exs

@@ -34,7 +34,7 @@ defmodule MobileAppBackend.Health.CacheTest do
           Health.Cache.handle_info(:check, %{cache: Cache})
         end)
 
-      assert msg =~ "cache=#{Cache} cache_health hits=4 misses=4 hit_rate=0.5"
+      assert msg =~ "cache=#{Cache} cache_health hits=4 misses=4"
     end
   end
 end