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Rails rendering extension for server-side html caching

CacheRocket improves fragment caching efficiency in Rails. CacheRocket allows caching more generic html fragments and allowing the contents of the cached fragments to be replaced with dynamic content. CacheRocket is a technique that may be used with other Rails caching strategies such as Russian Doll caching.

Install

Add this line to your Gemfile:

gem 'cache_rocket'

Add this line to a helper file, likely your ApplicationHelper:

include CacheRocket

Use

This gem allows you to cache a fragment of html and replace inner html. You cache the donut and replace the donut hole.

Assume you have some html that you would like to cache, but cannot because of some uncacheable code nested in the DOM. For example:

file.html.haml:
= render 'container'
_container.html.haml:
.lots
  .of
    .htmls
      = render 'inner'
_inner.html.haml:
= complicated_uncacheable_stuff

In the scenario above, you can't cache anything. With cache_rocket, you can. Replace render with render_cached in file, specify the partial to replace in container, and cache container:

file.html.haml:
= render_cached 'container', replace: 'inner'
_container.html.haml:
- cache 'container' do
  .lots
    .of
      .htmls
        = cache_replace_key 'inner'
_inner.html.haml:
= complicated_uncacheable_stuff

In this example, you could remove the _inner.html.haml file altogether, like so:

file.html.haml:
= render_cached 'container', replace: { inner: complicated_uncacheable_stuff }
_container.html.haml:
- cache 'container' do
  .lots
    .of
      .htmls
        = cache_replace_key 'inner'

Options

render_cached supports several styles of arguments:

Single partial to replace

render_cached 'container', replace: 'inner'

Array of partials to replace

render_cached 'container', replace: ['inner', 'footer']

Hash of keys to replace with values

render_cached 'container', replace: { key_name: a_helper_method(object) }

Block containing a hash of keys to replace with values

render_cached 'container' do
  { key_name: a_helper_method(object) }
end

Render a collection with hash of keys, using a Proc for each collection item

render_cached 'container', collection: objects,
  replace: { key_name: ->(object){ a_helper_method(object) } }

Render a collection with block syntax

render_cached 'container', collection: objects do
  { key_name: ->(object){ a_helper_method(object) } }
end

YMMV

cache_rocket is not magic. It should not be used in all situations. Benchmark your page load times before and after to see if it helps.

Benefits

More server-side caching

See the example above.

Use far less memory

Typically, one would key the users/bio partial on the user object like so:

users/bio.haml:
- cache [user, 'bio'] do
  .lots-of-htmls
    = user.bio

= render 'users/bio'

With 1000 users, there are 1000 cached items. This can use a lot of memory. Instead we can cache the users/bio partial once and replace the content we need using cache_replace. With 1000 users, we use 1/1000th the memory.

users/bio.haml:
- cache('users/bio') do
  .lots-of-htmls
    = cache_replace_key :bio

= render_cached 'users/bio', replace: { bio: user.bio }

Simpler cache keys

If you have a cache key containing multiple models, it will generally be very inefficient:

- cache(user, other_user) do
  = render 'common_interests'

If the cached content is rarely retrieved, cache_replace can help:

- cache('common_interests') do
  .htmls
    = cache_replace_key :something

= render 'common_interests', replace: { something: 'common_interests/inner' }

Faster first page loads

By caching common html, you ensure that you will render cached content the first time a model-dependent fragment is rendered. See the Use far less memory section above for an example.

References