Caching Strategies for Rails 8 Skill

Caching Strategies for Rails 8

Overview

Rails provides multiple caching layers:

Fragment caching: Cache view partials
Russian doll caching: Nested cache fragments
Low-level caching: Cache arbitrary data
HTTP caching: Browser and CDN caching
Query caching: Automatic within requests

Quick Start

# config/environments/development.rb
config.action_controller.perform_caching = true
config.cache_store = :memory_store

# config/environments/production.rb
config.cache_store = :solid_cache_store  # Rails 8 default
# OR
config.cache_store = :redis_cache_store, { url: ENV["REDIS_URL"] }

Enable caching in development:

bin/rails dev:cache

Cache Store Options

| Store | Use Case | Pros | Cons | |-------|----------|------|------| | :memory_store | Development | Fast, no setup | Not shared, limited size | | :solid_cache_store | Production (Rails 8) | Database-backed, no Redis | Slightly slower | | :redis_cache_store | Production | Fast, shared | Requires Redis | | :file_store | Simple production | Persistent, no Redis | Slow, not shared | | :null_store | Testing | No caching | N/A |

Fragment Caching

Basic Fragment Cache

<%# app/views/events/_event.html.erb %>
<% cache event do %>
  <article class="event-card">
    <h3><%= event.name %></h3>
    <p><%= event.description %></p>
    <time><%= l(event.event_date, format: :long) %></time>
    <%= render event.venue %>
  </article>
<% end %>

Cache Key Components

Rails generates cache keys from:

Model name
Model ID
updated_at timestamp
Template digest (automatic)

# Generated key example:
# views/events/123-20240115120000000000/abc123digest

Custom Cache Keys

<%# With version %>
<% cache [event, "v2"] do %>
  ...
<% end %>

<%# With user-specific content %>
<% cache [event, current_user] do %>
  ...
<% end %>

<%# With explicit key %>
<% cache "featured-events-#{Date.current}" do %>
  <%= render @featured_events %>
<% end %>

Russian Doll Caching

Nested caches where inner caches are reused when outer cache is invalidated:

<%# app/views/events/show.html.erb %>
<% cache @event do %>
  <h1><%= @event.name %></h1>

  <section class="vendors">
    <% @event.vendors.each do |vendor| %>
      <% cache vendor do %>
        <%= render partial: "vendors/card", locals: { vendor: vendor } %>
      <% end %>
    <% end %>
  </section>

  <section class="comments">
    <% @event.comments.each do |comment| %>
      <% cache comment do %>
        <%= render comment %>
      <% end %>
    <% end %>
  </section>
<% end %>

Use touch: true on belongs_to associations to cascade invalidation up the chain. See cache-invalidation.md for examples.

Collection Caching

Efficient Collection Rendering

<%# Caches each item individually %>
<%= render partial: "events/event", collection: @events, cached: true %>

<%# With custom cache key %>
<%= render partial: "events/event",
           collection: @events,
           cached: ->(event) { [event, current_user.admin?] } %>

Low-Level Caching

Use Rails.cache.fetch with a block for the most common pattern. See low-level-caching.md for:

Basic read/write/fetch examples
Caching in service objects
Caching in query objects
Instance variable memoization
Request-scoped memoization with CurrentAttributes

Cache Invalidation

Three strategies: time-based expiration, key-based expiration (using updated_at), and manual deletion. See cache-invalidation.md for:

Time-based and key-based expiration
Manual invalidation in model callbacks and services
Pattern-based deletion (delete_matched)
touch: true for Russian doll cascade
Built-in and custom counter caches

HTTP Caching

Use stale? for conditional GET (ETags/Last-Modified) and expires_in for Cache-Control headers. See http-caching-and-testing.md for full examples.

Testing Caching

Use a :caching metadata tag to enable caching in specs. See http-caching-and-testing.md for:

rails_helper.rb configuration
Testing cached view invalidation
Testing cache invalidation in services
Performance monitoring and instrumentation

Checklist

[ ] Cache store configured for environment
[ ] Fragment caching on expensive partials
[ ] touch: true on belongs_to for Russian doll
[ ] Collection caching with cached: true
[ ] Low-level caching for expensive queries
[ ] Cache invalidation strategy defined
[ ] Counter caches for counts
[ ] HTTP caching headers for API
[ ] Cache warming for cold starts (if needed)
[ ] Monitoring for hit/miss rates

References

low-level-caching.md - fetch/read/write, service objects, query objects, memoization
cache-invalidation.md - expiration strategies, manual invalidation, touch, counter caches
http-caching-and-testing.md - ETags, Cache-Control, spec configuration, monitoring

Agent Skills: Caching Strategies for Rails 8

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