fix: Performance degradation on Catalog Page

caching/api.py

@@ -0,0 +1,61 @@
+"""
+Interface for Django's caching API
+"""
+from dill import dumps, loads
+from django.core.cache import cache
+from django.db.models import Prefetch
+
+from courses.models import Course
+from ecommerce.models import Product
+
+
+def get_course_key(course_id):
+    """
+    Generates cache key for a course id.
+
+    Args:
+        course_id (int): id of a course.
+
+    Returns:
+        str: Cache for the given course id.
+    """
+    return f"course_id:{course_id}"
+
+
+def get_course_with_related_objects(course_id):
+    """
+    Gets course with related objects from cache if it is available
+    else fetch the course with related objects and add it to the cache.
+
+    Args:
+        course_id (int): id of a course.
+
+    Returns:
+        Course or None: Course with related objects or None.
+    """
+    cache_key = get_course_key(course_id)
+    course = cache.get(cache_key)
+    course = loads(course) if course else None
+    print("\n\n\nCOURSE FROM CACHE:", course)
+
+    if not course:
+        course = (
+            Course.objects.filter(id=course_id)
+            .select_related("program", "program__programpage")
+            .prefetch_related(
+                "courseruns",
+                Prefetch(
+                    "courseruns__products", Product.objects.with_ordered_versions()
+                ),
+            ).first()
+        )
+        if course:
+            print("\n\n\nAdding Course Cache for:", course_id)
+            cache.set(cache_key, dumps(course), 24 * 60 * 60)
+
+    return course
+
+
+def invalidate_course_cache(course_id):
+    cache_key = get_course_key(course_id)
+    cache.delete(cache_key)

cms/models.py

@@ -32,6 +32,7 @@
 from wagtail.snippets.models import register_snippet
 from wagtailmetadata.models import MetadataPageMixin
 
+from caching.api import get_course_with_related_objects
 from cms.api import filter_and_sort_catalog_pages
 from cms.blocks import (
     CourseRunCertificateOverrides,
@@ -976,17 +977,7 @@ def course_with_related_objects(self):
         """
         Gets the course with related objects.
         """
-        return (
-            Course.objects.filter(id=self.course_id)
-            .select_related("program", "program__programpage")
-            .prefetch_related(
-                "courseruns",
-                Prefetch(
-                    "courseruns__products", Product.objects.with_ordered_versions()
-                ),
-            )
-            .first()
-        )
+        return get_course_with_related_objects(self.course_id)
 
     def get_context(self, request, *args, **kwargs):
         # Hits a circular import at the top of the module

courses/signals.py

@@ -5,8 +5,11 @@
 from django.db.models.signals import post_save
 from django.dispatch import receiver
 
-from courses.models import CourseRunCertificate
+from caching.api import invalidate_course_cache
+from courses.models import CourseRunCertificate, Course, CourseRun, Program
 from courses.utils import generate_program_certificate
+from cms.models import ProgramPage
+from ecommerce.models import Product, ProductVersion
 
 
 @receiver(
@@ -25,3 +28,33 @@ def handle_create_course_run_certificate(
         program = instance.course_run.course.program
         if program:
             transaction.on_commit(lambda: generate_program_certificate(user, program))
+
+
+@receiver(post_save, sender=Course)
+@receiver(post_save, sender=CourseRun)
+@receiver(post_save, sender=Program)
+@receiver(post_save, sender=ProgramPage)
+@receiver(post_save, sender=Product)
+def handle_course_cache_invalidation(sender, instance, created, **kwargs):
+    if sender == Course and created:
+        print("\n\n\nCreated a course object. No Cache to invalidate")
+        return
+
+    course_ids = []
+    if sender == Course:
+        course_ids = [instance.id]
+    elif sender == CourseRun:
+        course_ids = [instance.course_id]
+    elif sender == Program:
+        course_ids = instance.courses.all().values_list('id', flat=True)
+    elif sender == ProgramPage:
+        course_ids = instance.program.courses.all().values_list('id', flat=True)
+    elif sender == Product:
+        if instance.content_type.model == CourseRun.__name__.lower():
+            course_run = instance.run_queryset.first()
+            course_ids = [course_run.id]
+
+    if course_ids:
+        print("\n\n\nClear cache for Course IDs:", course_ids)
+        for course_id in course_ids:
+            invalidate_course_cache(course_id)

requirements.in

@@ -50,3 +50,4 @@ wagtail==2.13.4
 wagtail-metadata==3.3.0
 zeep==3.4.0
 flaky==3.7.0
+dill==0.3.6

requirements.txt

@@ -1,6 +1,6 @@
 #
-# This file is autogenerated by pip-compile with python 3.9
-# To update, run:
+# This file is autogenerated by pip-compile with Python 3.9
+# by the following command:
 #
 #    pip-compile
 #
@@ -88,6 +88,8 @@ defusedxml==0.7.1
     #   python3-openid
     #   social-auth-core
     #   zeep
+dill==0.3.6
+    # via -r requirements.in
 dj-database-url==0.5.0
     # via -r requirements.in
 django==3.2.15