Cache invalidation strategies in Django

Introduction

Cache invalidation strategies help keep your cached data fresh and accurate. They decide when to update or remove stored data so users see the latest information.

When you want to update cached web pages after content changes.

When database records change and cached queries need refreshing.

When user-specific data in cache must reflect recent actions.

When you want to avoid showing outdated information to users.

When you want to improve performance but keep data reliable.

Syntax

Django

from django.core.cache import cache

# Example: Delete a cache key
cache.delete('my_key')

# Example: Set cache with timeout
cache.set('my_key', 'value', timeout=300)

# Example: Clear all cache
cache.clear()

Use cache.delete(key) to remove specific cached data.

Use timeout to set how long data stays cached before automatic invalidation.

Examples

Cache user profile data for 10 minutes (600 seconds).

Django

cache.set('user_42_profile', user_profile_data, timeout=600)

Remove cached user profile when it changes.

Django

cache.delete('user_42_profile')

Clear all cached data, useful after big updates.

Django

cache.clear()

Sample Program

This example caches a product list, then updates it by deleting the old cache and setting a new one. Finally, it prints the updated cached list.

Django

from django.core.cache import cache

# Simulate caching a product list
products = ['apple', 'banana', 'cherry']
cache.set('product_list', products, timeout=120)

# Later, product list changes
products.append('date')

# Invalidate old cache
cache.delete('product_list')

# Update cache with new list
cache.set('product_list', products, timeout=120)

# Retrieve and print cached product list
cached_products = cache.get('product_list')
print(cached_products)

Important Notes

Always delete or update cache when underlying data changes to avoid stale info.

Use timeouts to automatically expire cache if manual invalidation is missed.

Be careful with cache.clear() as it removes all cached data, which might affect performance.

Summary

Cache invalidation keeps cached data fresh and accurate.

Use cache.delete() to remove specific cached items.

Set timeouts to auto-expire cached data after some time.