Optimise for cache hits

Don't select/prefetch for listing, because we cache the entire listing item. This makes the main query more efficient, thus page loads faster.

website/blog/models.py

@@ -9,7 +9,7 @@ from wagtail.admin.panels import FieldPanel
 from wagtailautocomplete.edit_handlers import AutocompletePanel
 
 from website.common.models import BaseContentPage, BaseListingPage
-from website.common.utils import TocEntry, prefetch_for_listing
+from website.common.utils import TocEntry
 from website.common.views import ContentPageFeed
 from website.contrib.singleton_page.utils import SingletonPageCache
 
@@ -43,12 +43,11 @@ class BlogPostListPage(BaseListingPage):
         ]
 
     def get_listing_pages(self) -> models.QuerySet:
-        return prefetch_for_listing(
+        return (
             BlogPostPage.objects.descendant_of(self)
             .live()
             .public()
             .order_by("-date", "title")
-            .prefetch_related("tags")
         )
 
     @property
@@ -127,11 +126,10 @@ class BlogPostCollectionPage(BaseListingPage):
     subpage_types = [BlogPostPage]
 
     def get_listing_pages(self) -> models.QuerySet:
-        return prefetch_for_listing(
+        return (
             BlogPostPage.objects.child_of(self)
             .live()
             .public()
-            .prefetch_related("tags")
             .order_by("-date", "title")
         )
 

website/common/models.py

@@ -33,7 +33,6 @@ from .utils import (
     count_words,
     extract_text,
     get_table_of_contents,
-    prefetch_for_listing,
     truncate_string,
 )
 
@@ -190,9 +189,7 @@ class BaseListingPage(RoutablePageMixin, BaseContentPage):
         abstract = True
 
     def get_listing_pages(self) -> models.QuerySet:
-        return prefetch_for_listing(
-            self.get_children().live().public().specific().order_by("title")
-        )
+        return self.get_children().live().public().specific().order_by("title")
 
     def get_paginator_page(self) -> PaginatorPage:
         paginator = Paginator(self.get_listing_pages(), per_page=self.PAGE_SIZE)

website/common/templates/common/listing-item.html

@@ -1,22 +1,22 @@
 {% load wagtailcore_tags cache util_tags %}
 
-<article class="media listing-item">
-  <div class="columns">
-    <figure class="media-left column is-3 image-column">
-      {% if page.list_image_url %}
-        <a href="{% pageurl page %}" class="image">
-          <img src="{{ page.list_image_url }}" loading="lazy" decoding="async" />
-        </a>
-      {% endif %}
-    </figure>
-    <div class="media-content column">
-      <div>
-        <h2 class="title is-3"><a href="{% pageurl page %}">{{ page.title }}</a></h2>
-        {% include "common/content-details.html" %}
-        {% cache FRAGMENT_CACHE_TTL|jitter:FRAGMENT_CACHE_TTL_JITTER "summary" page.id request.is_preview %}
+{% cache FRAGMENT_CACHE_TTL|jitter:FRAGMENT_CACHE_TTL_JITTER "listing-item" page.id request.is_preview %}
+  <article class="media listing-item">
+    <div class="columns">
+      <figure class="media-left column is-3 image-column">
+        {% if page.list_image_url %}
+          <a href="{% pageurl page %}" class="image">
+            <img src="{{ page.list_image_url }}" loading="lazy" decoding="async" />
+          </a>
+        {% endif %}
+      </figure>
+      <div class="media-content column">
+        <div>
+          <h2 class="title is-3"><a href="{% pageurl page %}">{{ page.title }}</a></h2>
+          {% include "common/content-details.html" %}
           <p>{{ page.summary }}</p>
-        {% endcache %}
+        </div>
       </div>
     </div>
-  </div>
-</article>
+  </article>
+{% endcache %}

website/common/utils.py

@@ -87,16 +87,6 @@ def truncate_string(text: str, words: int) -> str:
     return " ".join(islice(smart_split(text), words))
 
 
-def prefetch_for_listing(queryset: PageQuerySet) -> PageQuerySet:
-    """
-    Prefetch a queryset ready for listing.
-
-    This should be a queryset method, but dealing with lots of
-    different page models is a pain.
-    """
-    return queryset.select_related("hero_image", "hero_unsplash_photo")
-
-
 def heading_id(heading: str) -> str:
     """
     Convert a heading into an identifier which is valid for a HTML id attribute

website/common/wagtail_hooks.py

@@ -6,7 +6,7 @@ from wagtail.models import Page
 
 from website.common.models import BasePage
 
-FRAGMENT_CACHES = {"summary", "content-details"}
+FRAGMENT_CACHES = {"listing-item", "content-details"}
 
 
 @hooks.register("after_edit_page")

website/search/models.py

@@ -10,7 +10,7 @@ from wagtail.models import Page
 from wagtail.search.utils import parse_query_string
 
 from website.common.models import BaseContentPage
-from website.common.utils import TocEntry, prefetch_for_listing
+from website.common.utils import TocEntry
 from website.home.models import HomePage
 
 from .serializers import MIN_SEARCH_LENGTH, SearchParamsSerializer
@@ -76,9 +76,7 @@ class SearchPage(RoutablePageMixin, BaseContentPage):
             results = paginator.page(page_num)
 
             # HACK: Search results aren't a queryset, so we can't call `.specific` on it. This forces it to one as efficiently as possible
-            results.object_list = prefetch_for_listing(
-                results.object_list.get_queryset().specific()
-            )
+            results.object_list = results.object_list.get_queryset().specific()
 
         except EmptyPage:
             raise Http404