optimise product queries: skip image blobs, limit listing preloads, add composite index

The listing preload (images: :image) was loading the full images table row
including the data BLOB column (~3MB per page). Now only loads :id and
:source_width. Listing preloads also limited to first 2 images (primary +
hover) since product cards don't use the rest. Added composite indexes on
(visible, status, inserted_at) and (visible, status, category) to eliminate
the TEMP B-TREE sort SQLite was doing.

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

lib/berrypod/products.ex

@@ -132,10 +132,19 @@ defmodule Berrypod.Products do
   # Storefront queries
   # =============================================================================
 
-  # Listing pages only need images (price/stock are denormalized on product)
-  @listing_preloads [images: :image]
-  # Detail page also needs variants for the variant selector
-  @detail_preloads [images: :image, variants: []]
+  # Image preload that skips the data blob — only loads :id and :source_width
+  # from the images table. The data column holds the raw image binary (up to 5MB
+  # per row) which is never used in rendering.
+  defp image_preload_query do
+    from(i in Berrypod.Media.Image, select: struct(i, [:id, :source_width]))
+  end
+
+  # Listing pages only need the first 2 images (primary + hover) and don't
+  # need variants (price/stock are denormalized on the product row).
+  defp listing_preloads do
+    pi_query = from(pi in ProductImage, where: pi.position <= 1, order_by: pi.position)
+    [images: {pi_query, image: image_preload_query()}]
+  end
 
   @doc """
   Gets a single visible, active product by slug with full preloads (for detail page).
@@ -143,8 +152,11 @@ defmodule Berrypod.Products do
   def get_visible_product(slug) do
     Product
     |> where([p], p.slug == ^slug and p.visible == true and p.status == "active")
-    |> preload(^@detail_preloads)
     |> Repo.one()
+    |> case do
+      nil -> nil
+      product -> Repo.preload(product, images: [image: image_preload_query()], variants: [])
+    end
   end
 
   @doc """
@@ -167,8 +179,8 @@ defmodule Berrypod.Products do
     |> apply_sort(opts[:sort])
     |> maybe_limit(opts[:limit])
     |> maybe_exclude(opts[:exclude])
-    |> preload(^@listing_preloads)
     |> Repo.all()
+    |> Repo.preload(listing_preloads())
   end
 
   @doc """
@@ -177,13 +189,15 @@ defmodule Berrypod.Products do
   Accepts the same filter/sort options plus `:page` and `:per_page`.
   """
   def list_visible_products_paginated(opts \\ []) do
-    Product
-    |> where([p], p.visible == true and p.status == "active")
-    |> apply_visible_filters(opts)
-    |> apply_sort(opts[:sort])
-    |> maybe_exclude(opts[:exclude])
-    |> preload(^@listing_preloads)
-    |> Berrypod.Pagination.paginate(page: opts[:page], per_page: opts[:per_page] || 24)
+    pagination =
+      Product
+      |> where([p], p.visible == true and p.status == "active")
+      |> apply_visible_filters(opts)
+      |> apply_sort(opts[:sort])
+      |> maybe_exclude(opts[:exclude])
+      |> Berrypod.Pagination.paginate(page: opts[:page], per_page: opts[:per_page] || 24)
+
+    %{pagination | items: Repo.preload(pagination.items, listing_preloads())}
   end
 
   @doc """
@@ -357,7 +371,7 @@ defmodule Berrypod.Products do
     |> apply_product_filters(opts)
     |> maybe_filter_in_stock(opts[:in_stock])
     |> apply_sort(opts[:sort])
-    |> preload([:provider_connection, images: :image, variants: []])
+    |> preload([:provider_connection, images: [image: ^image_preload_query()], variants: []])
     |> Repo.all()
   end
 
@@ -371,7 +385,7 @@ defmodule Berrypod.Products do
     |> apply_product_filters(opts)
     |> maybe_filter_in_stock(opts[:in_stock])
     |> apply_sort(opts[:sort])
-    |> preload([:provider_connection, images: :image, variants: []])
+    |> preload([:provider_connection, images: [image: ^image_preload_query()], variants: []])
     |> Berrypod.Pagination.paginate(page: opts[:page], per_page: opts[:per_page] || 25)
   end
 
@@ -397,6 +411,27 @@ defmodule Berrypod.Products do
     |> Repo.get(id)
   end
 
+  @doc """
+  Gets a product by ID with admin preloads (provider, images, variants).
+
+  Excludes image blob data.
+  """
+  def get_product_with_preloads(id) do
+    Product
+    |> Repo.get(id)
+    |> case do
+      nil ->
+        nil
+
+      product ->
+        Repo.preload(product, [
+          :provider_connection,
+          images: [image: image_preload_query()],
+          variants: []
+        ])
+    end
+  end
+
   @doc """
   Gets a single product by slug.
   """
@@ -817,7 +852,7 @@ defmodule Berrypod.Products do
   def get_variants_with_products(variant_ids) when is_list(variant_ids) do
     from(v in ProductVariant,
       where: v.id in ^variant_ids,
-      preload: [product: [images: :image]]
+      preload: [product: [images: [image: ^image_preload_query()]]]
     )
     |> Repo.all()
     |> Map.new(&{&1.id, &1})

lib/berrypod/search.ex

@@ -11,7 +11,15 @@ defmodule Berrypod.Search do
   alias Berrypod.Products.Product
   alias Berrypod.Repo
 
-  @listing_preloads [images: :image]
+  # Search results only need the first 2 images (card display) and only
+  # source_width from the images table — no blob data.
+  defp listing_preloads do
+    alias Berrypod.Products.ProductImage
+
+    image_query = from(i in Berrypod.Media.Image, select: struct(i, [:id, :source_width]))
+    pi_query = from(pi in ProductImage, where: pi.position <= 1, order_by: pi.position)
+    [images: {pi_query, image: image_query}]
+  end
 
   # BM25 column weights: title(10), category(5), variant_info(3), description(1)
   @bm25_weights "10.0, 5.0, 3.0, 1.0"
@@ -126,8 +134,8 @@ defmodule Berrypod.Search do
         Product
         |> where([p], p.id in ^product_ids)
         |> where([p], p.visible == true and p.status == "active")
-        |> preload(^@listing_preloads)
         |> Repo.all()
+        |> Repo.preload(listing_preloads())
         |> Map.new(&{&1.id, &1})
 
       Enum.flat_map(product_ids, fn id ->
@@ -148,8 +156,8 @@ defmodule Berrypod.Search do
     |> where([p], like(p.title, ^pattern) or like(p.category, ^pattern))
     |> order_by([p], p.title)
     |> limit(20)
-    |> preload(^@listing_preloads)
     |> Repo.all()
+    |> Repo.preload(listing_preloads())
   end
 
   defp sanitize_like(input) do

lib/berrypod/theme/preview_data.ex

@@ -361,7 +361,7 @@ defmodule Berrypod.Theme.PreviewData do
     Products.list_products(
       visible: true,
       status: "active",
-      preload: [images: :image, variants: []]
+      preload: [:images, :variants]
     )
   end
 

lib/berrypod_web/live/admin/product_show.ex

@@ -7,7 +7,7 @@ defmodule BerrypodWeb.Admin.ProductShow do
 
   @impl true
   def mount(%{"id" => id}, _session, socket) do
-    case Products.get_product(id, preload: [:provider_connection, images: :image, variants: []]) do
+    case Products.get_product_with_preloads(id) do
       nil ->
         socket =
           socket

lib/berrypod_web/live/admin/products.ex

@@ -64,7 +64,7 @@ defmodule BerrypodWeb.Admin.Products do
   @impl true
   def handle_event("toggle_visibility", %{"id" => id}, socket) do
     product =
-      Products.get_product(id, preload: [:provider_connection, images: :image, variants: []])
+      Products.get_product_with_preloads(id)
 
     case Products.toggle_visibility(product) do
       {:ok, updated} ->

priv/repo/migrations/20260302171616_add_products_listing_indexes.exs

@@ -0,0 +1,14 @@
+defmodule Berrypod.Repo.Migrations.AddProductsListingIndexes do
+  use Ecto.Migration
+
+  def change do
+    # Composite covering index for the main listing query:
+    # WHERE visible = 1 AND status = 'active' ORDER BY inserted_at DESC
+    # Replaces the individual visible + status indexes for this pattern
+    # and eliminates the TEMP B-TREE sort SQLite was doing.
+    create index(:products, [:visible, :status, :inserted_at])
+
+    # Filtered listing by category (second most common query pattern)
+    create index(:products, [:visible, :status, :category])
+  end
+end