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