cache settings, categories, and media in ETS to cut per-request DB queries

Every shop page load was triggering ~18 DB queries for data that rarely
changes (theme settings, nav items, categories, shipping countries, logo,
header image). On a shared-cpu-1x Fly machine with SQLite this was the
primary performance bottleneck.

- Add SettingsCache GenServer+ETS for all non-encrypted settings
- Cache list_categories() with single-query N+1 fix (correlated subquery)
- Cache list_available_countries_with_names() in shipping
- Cache Media.get_logo() and Media.get_header()
- Remove duplicate LoadTheme plug from :shop and :admin pipelines
- Invalidate caches on writes (put_setting, product sync, media upload)
- Clear caches between tests via DataCase/ConnCase setup

Per-page queries reduced from ~18 to ~2.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/berrypod/application.ex

@@ -36,6 +36,8 @@ defmodule Berrypod.Application do
       Berrypod.Images.VariantCache,
       # Start to serve requests
       BerrypodWeb.Endpoint,
+      # Settings cache - all non-encrypted settings in ETS (must warm before CSSCache)
+      Berrypod.Settings.SettingsCache,
       # Theme CSS cache - must start after Endpoint for static_path/1 to work
       Berrypod.Theme.CSSCache,
       # Page definition cache - loads page block lists into ETS

lib/berrypod/images/optimizer.ex

@@ -192,7 +192,18 @@ defmodule Berrypod.Images.Optimizer do
       widths = applicable_widths(source_width)
 
       all_tasks =
-        [fn -> generate_variant_to_dir(vips_image, output_basename, output_dir, "thumb", :jpg, @thumb_size) end] ++
+        [
+          fn ->
+            generate_variant_to_dir(
+              vips_image,
+              output_basename,
+              output_dir,
+              "thumb",
+              :jpg,
+              @thumb_size
+            )
+          end
+        ] ++
           for w <- widths, fmt <- @pregenerated_formats do
             fn -> generate_variant_to_dir(vips_image, output_basename, output_dir, w, fmt, w) end
           end
@@ -202,6 +213,7 @@ defmodule Berrypod.Images.Optimizer do
         timeout: :timer.seconds(120)
       )
       |> Stream.run()
+
       {:ok, source_width}
     end
   rescue

lib/berrypod/media.ex

@@ -34,6 +34,7 @@ defmodule Berrypod.Media do
           OptimizeWorker.enqueue(image.id)
         end
 
+        invalidate_media_cache(image.image_type)
         {:ok, image}
 
       error ->
@@ -122,12 +123,24 @@ defmodule Berrypod.Media do
 
   """
   def get_logo do
+    alias Berrypod.Settings.SettingsCache
+
+    case SettingsCache.get_cached(:logo) do
+      {:ok, logo} ->
+        logo
+
+      :miss ->
+        logo =
           Repo.one(
             from i in ImageSchema,
               where: i.image_type == "logo",
               order_by: [desc: i.inserted_at],
               limit: 1
           )
+
+        SettingsCache.put_cached(:logo, logo)
+        logo
+    end
   end
 
   @doc """
@@ -140,12 +153,24 @@ defmodule Berrypod.Media do
 
   """
   def get_header do
+    alias Berrypod.Settings.SettingsCache
+
+    case SettingsCache.get_cached(:header) do
+      {:ok, header} ->
+        header
+
+      :miss ->
+        header =
           Repo.one(
             from i in ImageSchema,
               where: i.image_type == "header",
               order_by: [desc: i.inserted_at],
               limit: 1
           )
+
+        SettingsCache.put_cached(:header, header)
+        header
+    end
   end
 
   @doc """
@@ -158,7 +183,14 @@ defmodule Berrypod.Media do
 
   """
   def delete_image(%ImageSchema{} = image) do
-    Repo.delete(image)
+    result = Repo.delete(image)
+
+    case result do
+      {:ok, _} -> invalidate_media_cache(image.image_type)
+      _ -> :ok
+    end
+
+    result
   end
 
   @doc """
@@ -419,4 +451,12 @@ defmodule Berrypod.Media do
     )
     |> Repo.insert()
   end
+
+  defp invalidate_media_cache("logo"),
+    do: Berrypod.Settings.SettingsCache.invalidate_cached(:logo)
+
+  defp invalidate_media_cache("header"),
+    do: Berrypod.Settings.SettingsCache.invalidate_cached(:header)
+
+  defp invalidate_media_cache(_), do: :ok
 end

lib/berrypod/products.ex

@@ -190,38 +190,76 @@ defmodule Berrypod.Products do
   Lists distinct categories from visible, active products.
   Returns a list of `%{name, slug, image_url}` where `image_url` is the
   first product image for a representative product in that category.
+
+  Results are cached in ETS and invalidated when products change.
   """
   def list_categories do
+    alias Berrypod.Settings.SettingsCache
+
+    case SettingsCache.get_cached(:categories) do
+      {:ok, categories} ->
+        categories
+
+      :miss ->
+        categories = do_list_categories()
+        SettingsCache.put_cached(:categories, categories)
+        categories
+    end
+  end
+
+  # Single query: categories with their first product image (by position).
+  # Uses a correlated subquery to pick the lowest-position image per category,
+  # replacing the previous N+1 pattern.
+  defp do_list_categories do
+    # Categories that have at least one product image
+    with_images =
+      from(p in Product,
+        join: pi in ProductImage,
+        on: pi.product_id == p.id,
+        where: p.visible == true and p.status == "active" and not is_nil(p.category),
+        where:
+          pi.id ==
+            fragment(
+              """
+              (SELECT pi2.id FROM product_images pi2
+               JOIN products p2 ON pi2.product_id = p2.id
+               WHERE p2.category = ? AND p2.visible = 1 AND p2.status = 'active'
+               ORDER BY pi2.position ASC LIMIT 1)
+              """,
+              p.category
+            ),
+        group_by: p.category,
+        order_by: p.category,
+        select: {p.category, pi.image_id, pi.src}
+      )
+      |> Repo.all()
+
+    categories_with_images = MapSet.new(with_images, &elem(&1, 0))
+
+    # Categories without any images (still need to appear in the list)
+    without_images =
       from(p in Product,
         where: p.visible == true and p.status == "active" and not is_nil(p.category),
+        where: p.category not in ^MapSet.to_list(categories_with_images),
         select: p.category,
         distinct: true,
         order_by: p.category
       )
       |> Repo.all()
-    |> Enum.map(fn name ->
-      image_url = category_image_url(name)
-      %{name: name, slug: Slug.slugify(name), image_url: image_url}
-    end)
+      |> Enum.map(&{&1, nil, nil})
+
+    (with_images ++ without_images)
+    |> Enum.sort_by(&elem(&1, 0))
+    |> Enum.map(fn {name, image_id, src} ->
+      image_url =
+        cond do
+          not is_nil(image_id) -> "/image_cache/#{image_id}-400.webp"
+          is_binary(src) -> src
+          true -> nil
         end
 
-  defp category_image_url(category_name) do
-    from(pi in ProductImage,
-      join: p in Product,
-      on: pi.product_id == p.id,
-      where:
-        p.visible == true and p.status == "active" and
-          p.category == ^category_name,
-      order_by: [asc: pi.position],
-      limit: 1,
-      select: {pi.image_id, pi.src}
-    )
-    |> Repo.one()
-    |> case do
-      {id, _src} when not is_nil(id) -> "/image_cache/#{id}-400.webp"
-      {_, src} when is_binary(src) -> src
-      _ -> nil
-    end
+      %{name: name, slug: Slug.slugify(name), image_url: image_url}
+    end)
   end
 
   @doc """
@@ -400,9 +438,17 @@ defmodule Berrypod.Products do
   Updates storefront-only fields (visibility and category).
   """
   def update_storefront(%Product{} = product, attrs) do
+    result =
       product
       |> Product.storefront_changeset(attrs)
       |> Repo.update()
+
+    case result do
+      {:ok, _} -> Berrypod.Settings.SettingsCache.invalidate_cached(:categories)
+      _ -> :ok
+    end
+
+    result
   end
 
   @doc """
@@ -430,7 +476,14 @@ defmodule Berrypod.Products do
       source: "auto_product_deleted"
     })
 
-    Repo.delete(product)
+    result = Repo.delete(product)
+
+    case result do
+      {:ok, _} -> Berrypod.Settings.SettingsCache.invalidate_cached(:categories)
+      _ -> :ok
+    end
+
+    result
   end
 
   @doc """

lib/berrypod/settings.ex

@@ -5,7 +5,7 @@ defmodule Berrypod.Settings do
 
   import Ecto.Query, warn: false
   alias Berrypod.Repo
-  alias Berrypod.Settings.{Setting, ThemeSettings}
+  alias Berrypod.Settings.{Setting, SettingsCache, ThemeSettings}
   alias Berrypod.Vault
 
   @doc """
@@ -18,11 +18,17 @@ defmodule Berrypod.Settings do
 
   """
   def get_setting(key, default \\ nil) do
+    case SettingsCache.get(key) do
+      {:ok, value} ->
+        value
+
+      :miss ->
         case fetch_setting(key) do
           {:ok, setting} -> decode_value(setting)
           :not_found -> default
         end
     end
+  end
 
   @doc """
   Sets a setting value by key.
@@ -36,12 +42,24 @@ defmodule Berrypod.Settings do
   def put_setting(key, value, value_type \\ "string") do
     encoded_value = encode_value(value, value_type)
 
+    result =
       %Setting{key: key}
       |> Setting.changeset(%{key: key, value: encoded_value, value_type: value_type})
       |> Repo.insert(
         on_conflict: {:replace, [:value, :value_type, :updated_at]},
         conflict_target: :key
       )
+
+    case result do
+      {:ok, _} ->
+        SettingsCache.invalidate()
+        SettingsCache.warm()
+
+      _ ->
+        :ok
+    end
+
+    result
   end
 
   @doc """
@@ -154,10 +172,16 @@ defmodule Berrypod.Settings do
   Deletes a setting by key.
   """
   def delete_setting(key) do
+    result =
       case fetch_setting(key) do
         {:ok, setting} -> Repo.delete(setting)
         :not_found -> :ok
       end
+
+    SettingsCache.invalidate()
+    SettingsCache.warm()
+
+    result
   end
 
   @doc """

lib/berrypod/settings/settings_cache.ex

@@ -0,0 +1,162 @@
+defmodule Berrypod.Settings.SettingsCache do
+  @moduledoc """
+  GenServer that maintains an ETS table for caching settings and computed results.
+
+  Settings are loaded once from the DB on startup and served from ETS on every
+  request. The cache is invalidated (and immediately rewarmed) whenever a setting
+  is written via `Settings.put_setting/3` or `Settings.delete_setting/1`.
+
+  Also supports caching computed results (categories, shipping countries, etc.)
+  under `{:cached, key}` tuple keys. These are populated lazily and invalidated
+  explicitly when the underlying data changes.
+  """
+
+  use GenServer
+
+  @table_name :settings_cache
+
+  ## Client API — settings
+
+  def start_link(opts) do
+    GenServer.start_link(__MODULE__, opts, name: __MODULE__)
+  end
+
+  @doc """
+  Gets a cached setting by key.
+
+  Returns `{:ok, value}` if found, or `:miss` if the cache hasn't been warmed
+  or the key doesn't exist.
+  """
+  def get(key) do
+    case :ets.lookup(@table_name, :all_settings) do
+      [{:all_settings, map}] ->
+        case Map.fetch(map, key) do
+          {:ok, value} -> {:ok, value}
+          :error -> :miss
+        end
+
+      [] ->
+        :miss
+    end
+  rescue
+    ArgumentError -> :miss
+  end
+
+  @doc """
+  Gets a cached setting by key, returning a default on miss.
+  """
+  def get(key, default) do
+    case get(key) do
+      {:ok, value} -> value
+      :miss -> default
+    end
+  end
+
+  @doc """
+  Invalidates the settings map, forcing a reload on next warm.
+  """
+  def invalidate do
+    :ets.delete(@table_name, :all_settings)
+    :ok
+  rescue
+    ArgumentError -> :ok
+  end
+
+  @doc """
+  Warms the cache by loading all non-encrypted settings from the DB.
+  """
+  def warm do
+    alias Berrypod.Repo
+    alias Berrypod.Settings.Setting
+    import Ecto.Query
+
+    settings = Repo.all(from s in Setting, where: s.value_type != "encrypted")
+
+    map =
+      Map.new(settings, fn setting ->
+        {setting.key, decode_value(setting)}
+      end)
+
+    :ets.insert(@table_name, {:all_settings, map})
+    :ok
+  end
+
+  ## Client API — computed results (categories, countries, etc.)
+
+  @doc """
+  Gets a cached computed result by key.
+
+  Returns `{:ok, value}` if found, or `:miss` if not yet cached.
+  """
+  def get_cached(key) do
+    case :ets.lookup(@table_name, {:cached, key}) do
+      [{{:cached, ^key}, value}] -> {:ok, value}
+      [] -> :miss
+    end
+  rescue
+    ArgumentError -> :miss
+  end
+
+  @doc """
+  Caches a computed result under the given key.
+  """
+  def put_cached(key, value) do
+    :ets.insert(@table_name, {{:cached, key}, value})
+    :ok
+  rescue
+    ArgumentError -> :ok
+  end
+
+  @doc """
+  Invalidates a single cached computed result.
+  """
+  def invalidate_cached(key) do
+    :ets.delete(@table_name, {:cached, key})
+    :ok
+  rescue
+    ArgumentError -> :ok
+  end
+
+  @doc """
+  Clears all cached data (settings and computed results). For tests.
+  """
+  def invalidate_all do
+    :ets.delete_all_objects(@table_name)
+    :ok
+  rescue
+    ArgumentError -> :ok
+  end
+
+  ## Server Callbacks
+
+  @impl true
+  def init(_opts) do
+    :ets.new(@table_name, [
+      :set,
+      :public,
+      :named_table,
+      read_concurrency: true,
+      write_concurrency: false
+    ])
+
+    {:ok, %{}, {:continue, :warm}}
+  end
+
+  @impl true
+  def handle_continue(:warm, state) do
+    try do
+      warm()
+    rescue
+      _ -> :ok
+    end
+
+    {:noreply, state}
+  end
+
+  ## Private — mirrors Settings.decode_value/1 for non-encrypted types
+
+  defp decode_value(%{value: value, value_type: "json"}), do: Jason.decode!(value)
+  defp decode_value(%{value: value, value_type: "integer"}), do: String.to_integer(value)
+  defp decode_value(%{value: value, value_type: "boolean"}), do: value == "true"
+  defp decode_value(%{value: value, value_type: "string"}), do: value
+end

lib/berrypod/shipping.ex

@@ -114,6 +114,7 @@ defmodule Berrypod.Shipping do
       )
 
     Logger.info("Upserted #{count} shipping rates for connection #{provider_connection_id}")
+    Berrypod.Settings.SettingsCache.invalidate_cached(:countries_with_names)
     {:ok, count}
   end
 
@@ -343,9 +344,21 @@ defmodule Berrypod.Shipping do
   sorted by name.
   """
   def list_available_countries_with_names do
+    alias Berrypod.Settings.SettingsCache
+
+    case SettingsCache.get_cached(:countries_with_names) do
+      {:ok, countries} ->
+        countries
+
+      :miss ->
+        countries =
           list_available_countries()
           |> Enum.map(fn code -> {code, country_name(code)} end)
           |> Enum.sort_by(&elem(&1, 1))
+
+        SettingsCache.put_cached(:countries_with_names, countries)
+        countries
+    end
   end
 
   @doc """

lib/berrypod/sync/product_sync_worker.ex

@@ -129,6 +129,10 @@ defmodule Berrypod.Sync.ProductSyncWorker do
       # Rebuild search index after successful sync
       Berrypod.Search.rebuild_index()
 
+      # Invalidate cached categories and countries (products/rates may have changed)
+      Berrypod.Settings.SettingsCache.invalidate_cached(:categories)
+      Berrypod.Settings.SettingsCache.invalidate_cached(:countries_with_names)
+
       :ok
     else
       {:error, reason} = error ->

lib/berrypod_web/router.ex

@@ -42,13 +42,11 @@ defmodule BerrypodWeb.Router do
 
   pipeline :shop do
     plug :put_root_layout, html: {BerrypodWeb.Layouts, :shop_root}
-    plug BerrypodWeb.Plugs.LoadTheme
     plug BerrypodWeb.Plugs.Analytics
   end
 
   pipeline :admin do
     plug :put_root_layout, html: {BerrypodWeb.Layouts, :admin_root}
-    plug BerrypodWeb.Plugs.LoadTheme
   end
 
   # ── Routes without the :browser pipeline ──────────────────────────

test/support/conn_case.ex

@@ -33,6 +33,7 @@ defmodule BerrypodWeb.ConnCase do
 
   setup tags do
     Berrypod.DataCase.setup_sandbox(tags)
+    Berrypod.Settings.SettingsCache.invalidate_all()
     {:ok, conn: Phoenix.ConnTest.build_conn()}
   end
 

test/support/data_case.ex

@@ -29,6 +29,7 @@ defmodule Berrypod.DataCase do
 
   setup tags do
     Berrypod.DataCase.setup_sandbox(tags)
+    Berrypod.Settings.SettingsCache.invalidate_all()
     :ok
   end