Changes (#76)

* Implement caching for homepage data and signals to improve performance

- Added caching for categories, recent questions, active questions, slider questions, spam questions, and category question mapping in views.
- Introduced a cache invalidation mechanism in signals for questions and answers.
- Updated the settings to include cache configuration.
- Enhanced template tags to cache total question and answer counts.
- Refactored the category image retrieval to utilize caching.

* Update caching configuration and improve homepage data retrieval

- Changed cache backend to Memcached and added a file cache option in settings.
- Increased HOME_CACHE_TIMEOUT to 3600 seconds for better performance.
- Refactored homepage data retrieval functions to accept a base queryset, enhancing flexibility and efficiency.
- Updated calls to caching functions to utilize the new base queryset parameter.

* Refactor caching configuration to support Memcached and local memory fallback

- Updated the caching settings to use Memcached if available, otherwise default to local memory for development.
- Simplified cache backend configuration by defining a single variable for the default cache settings.

* Add make_cache_key function for Memcached-safe cache key generation

- Introduced a new helper function, make_cache_key, to create cache keys that comply with Memcached restrictions.
- Updated the category image retrieval function to utilize the new caching mechanism, enhancing cache key normalization and safety.

Author: Kushagra1122

forums/settings.py

@@ -235,12 +235,32 @@
     'compressor.filters.css_default.CssAbsoluteFilter',
     'compressor.filters.cssmin.CSSMinFilter',
 )
-"""CACHES = {
-    'default': {
+
+# Use Memcached when the memcache package is available; otherwise use local memory
+# (e.g. for local development without Memcached).
+try:
+    import memcache  # noqa: F401
+    _default_cache = {
+        'BACKEND': 'django.core.cache.backends.memcached.MemcachedCache',
+        'LOCATION': 'localhost:11211',
+        'TIMEOUT': 3600 * 24,
+        'KEY_PREFIX': 'forums',
+    }
+except ImportError:
+    _default_cache = {
         'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
-        'LOCATION': 'unique-snowflake'
+        'TIMEOUT': 3600 * 24,
+        'KEY_PREFIX': 'forums',
     }
-}"""
+
+CACHES = {
+    'default': _default_cache,
+    'file_cache': {
+        'BACKEND': 'django.core.cache.backends.db.DatabaseCache',
+        'LOCATION': 'topper_cache_table',
+        'TIMEOUT': 3600 * 24 * 30,
+    },
+}
 
 COMPRESS_ENABLED = True
 

website/apps.py

@@ -1,11 +1,56 @@
 from django.apps import AppConfig
-from django.db.models.signals import post_save
+from django.db.models.signals import post_save, post_delete
+
 
 class WebsiteConfig(AppConfig):
     name = 'website'
 
     def ready(self):
-        from .models import Answer, AnswerComment
-        from .signals import last_active_signal_from_answer, last_active_signal_from_reply
-        post_save.connect(last_active_signal_from_answer, sender=Answer, dispatch_uid='trigger_last_active_answer')
-        post_save.connect(last_active_signal_from_reply, sender=AnswerComment, dispatch_uid='trigger_last_active_reply')
+        from .models import Question, Answer, AnswerComment
+        from .signals import (
+            last_active_signal_from_answer,
+            last_active_signal_from_reply,
+            home_cache_invalidator,
+        )
+
+        post_save.connect(
+            last_active_signal_from_answer,
+            sender=Answer,
+            dispatch_uid='trigger_last_active_answer',
+        )
+        post_save.connect(
+            last_active_signal_from_reply,
+            sender=AnswerComment,
+            dispatch_uid='trigger_last_active_reply',
+        )
+
+        post_save.connect(
+            home_cache_invalidator,
+            sender=Question,
+            dispatch_uid='home_cache_invalidator_question_save',
+        )
+        post_delete.connect(
+            home_cache_invalidator,
+            sender=Question,
+            dispatch_uid='home_cache_invalidator_question_delete',
+        )
+        post_save.connect(
+            home_cache_invalidator,
+            sender=Answer,
+            dispatch_uid='home_cache_invalidator_answer_save',
+        )
+        post_delete.connect(
+            home_cache_invalidator,
+            sender=Answer,
+            dispatch_uid='home_cache_invalidator_answer_delete',
+        )
+        post_save.connect(
+            home_cache_invalidator,
+            sender=AnswerComment,
+            dispatch_uid='home_cache_invalidator_answercomment_save',
+        )
+        post_delete.connect(
+            home_cache_invalidator,
+            sender=AnswerComment,
+            dispatch_uid='home_cache_invalidator_answercomment_delete',
+        )

website/helpers.py

@@ -1,4 +1,5 @@
 import re
+import hashlib
 from website.models import Question
 from nltk.corpus import stopwords 
 from nltk.tokenize import word_tokenize
@@ -33,6 +34,45 @@ def get_video_info(path):
     return info_m
 
 
+def make_cache_key(prefix, *parts):
+    """
+    Create a Memcached-safe cache key by hashing if necessary.
+    
+    Memcached has restrictions on cache keys:
+    - No spaces or control characters
+    - Maximum 250 bytes length
+    
+    This function constructs a key from prefix and parts, and hashes it
+    if it contains spaces, special characters, or exceeds 200 bytes (safe limit).
+    
+    Args:
+        prefix: The key prefix (e.g., 'category_image')
+        *parts: Variable parts to include in the key (e.g., category name)
+    
+    Returns:
+        A normalized cache key string safe for Memcached
+    """
+    # Construct the key string
+    key_parts = [str(part) for part in parts]
+    key_string = ':'.join([prefix] + key_parts)
+    
+    # Check if key needs hashing:
+    # 1. Contains spaces or control characters
+    # 2. Exceeds 200 bytes (safe limit, Memcached allows 250)
+    needs_hashing = (
+        ' ' in key_string or
+        '\x00' in key_string or
+        len(key_string.encode('utf-8')) > 200
+    )
+    
+    if needs_hashing:
+        # Hash the entire key and use hex digest (64 chars, always safe)
+        key_hash = hashlib.sha256(key_string.encode('utf-8')).hexdigest()
+        return f'{prefix}:{key_hash}'
+    
+    return key_string
+
+
 def prettify(string):
     string = string.lower()
     string = string.replace('-', ' ')

website/signals.py

@@ -1,13 +1,38 @@
 from django.utils import timezone
+from django.core.cache import cache
+
+
+HOME_CACHE_KEYS = [
+    'home:categories',
+    'home:recent_questions',
+    'home:active_questions',
+    'home:slider_questions',
+    'home:spam_questions',
+    'home:category_question_map',
+    'stats:total_questions',
+    'stats:total_answers',
+]
+
+
+def clear_home_cache():
+    cache.delete_many(HOME_CACHE_KEYS)
+
 
 def last_active_signal_from_answer(sender, instance, created, **kwargs):
     if created or not created:
         instance.question.last_active = timezone.now()
         instance.question.last_post_by = instance.uid
         instance.question.save()
+    clear_home_cache()
+
 
 def last_active_signal_from_reply(sender, instance, created, **kwargs):
     if created or not created:
         instance.answer.question.last_active = timezone.now()
         instance.answer.question.last_post_by = instance.uid
-        instance.answer.question.save()
+        instance.answer.question.save()
+    clear_home_cache()
+
+
+def home_cache_invalidator(sender, instance, **kwargs):
+    clear_home_cache()

website/templatetags/count_tags.py

@@ -1,4 +1,5 @@
 from django import template
+from django.core.cache import cache
 
 from website.models import Question, Answer
 
@@ -86,7 +87,13 @@ def div(value, arg=1):
 
 # retriving total number of questions
 def total_question_count():
+    cache_key = 'stats:total_questions'
+    count = cache.get(cache_key)
+    if count is not None:
+        return count
+
     count = Question.objects.filter(status=1).count()
+    cache.set(cache_key, count, 10)
     return count
 
 
@@ -95,7 +102,13 @@ def total_question_count():
 
 # retriving total number of answers
 def total_answer_count():
+    cache_key = 'stats:total_answers'
+    count = cache.get(cache_key)
+    if count is not None:
+        return count
+
     count = Answer.objects.filter(question__status=1).count()
+    cache.set(cache_key, count, 10)
     return count
 
 

website/templatetags/helpers.py

@@ -1,20 +1,29 @@
 from django import template
+from django.core.cache import cache
 
-# from website.models import Question, Answer, Notification
-from website.helpers import prettify
+from website.helpers import prettify, make_cache_key
 from django.conf import settings
 import os.path
 
 register = template.Library()
 
 
 def get_category_image(category):
+    cache_key = make_cache_key('category_image', category)
+    cached = cache.get(cache_key)
+    if cached is not None:
+        return cached
+
     base_path = settings.BASE_DIR + '/static/website/images/'
     file_name = category.replace(' ', '-') + '.jpg'
     file_path = base_path + file_name
     if os.path.isfile(file_path):
-        return 'website/images/' + file_name
-    return False
+        value = 'website/images/' + file_name
+    else:
+        value = False
+
+    cache.set(cache_key, value, 3600)
+    return value
 
 
 register.filter('get_category_image', get_category_image)