How to Use Caching in Rails for Faster Web Apps

In Rails, you use caches_action, caches_page, or low-level caching methods like Rails.cache.fetch to store data or views temporarily. This reduces repeated work and speeds up your app by reusing stored results instead of recalculating them.

Syntax

Rails provides several caching methods:

• Rails.cache.fetch(key) { block }: Stores and retrieves cached data by a key.
• caches_action :action_name: Caches the entire output of a controller action.
• caches_page :action_name: Caches the full HTML page for an action (legacy, less used).

Use Rails.cache.fetch for flexible, low-level caching of any data.

ruby

Rails.cache.fetch('my_key') do
  # Expensive operation
  User.count
end

Example

This example shows how to cache a list of users count to avoid hitting the database repeatedly.

ruby

class UsersController < ApplicationController
  def index
    @user_count = Rails.cache.fetch('user_count', expires_in: 5.minutes) do
      User.count
    end
  end
end

Output

When you visit the index page, the first request queries the database and caches the count. Subsequent requests within 5 minutes use the cached count, speeding up response time.

Common Pitfalls

Common mistakes when using caching in Rails include:

• Not setting expiration times, causing stale data.
• Using page caching (caches_page) in apps with dynamic content or authentication.
• Forgetting to expire or clear cache when data changes.
• Over-caching complex objects that consume too much memory.

Always plan cache expiration and invalidation carefully.

ruby

## Wrong: No expiration, stale data
Rails.cache.fetch('user_count') { User.count }

## Right: Set expiration to refresh cache
Rails.cache.fetch('user_count', expires_in: 10.minutes) { User.count }

Quick Reference

Caching Method	Use Case	Notes
Rails.cache.fetch	Cache any data with a key	Flexible, supports expiration
caches_action	Cache full controller action output	Good for static or rarely changing pages
caches_page	Cache full HTML page	Legacy, not recommended for dynamic content
expire_fragment	Expire cached fragments	Use to clear cache when data changes

Key Takeaways

Use Rails.cache.fetch with expiration to cache data safely and efficiently.

Avoid page caching for dynamic or user-specific content.

Always plan cache expiration and invalidation to prevent stale data.

Use action caching for full action output when content changes infrequently.

Test caching behavior to ensure it improves performance without breaking updates.