scoped_cache_keys

Add scoped_cache_key / expire_scoped_cache_key to your models for caching/sweeping of model-related caches.

Overview

scoped_cache_keys enables you to "scope" multiple cache entries together, such that they can be expired together in a single operation.

This saves the trouble of having to delete several individual cache entries, and improves the consistency of your cache entries by having them all expire together.

Model-related caches in a Rails application often consist of multiple cache entries, which should be consistent with each other.

For instance, you might have a cache entry which is a key->value mapping for a model, but another cache entry which is a value->key mapping.

Install

gem "scoped_cache_keys"

Usage

To use scoped_cached_keys, use include ScopedCacheKeys in your model declaration:

class User < ActiveRecord::Base
  include ScopedCacheKeys
  ...
end

scoped_cache_key

The scoped_cache_key method returns a key that will change whenever expire_scoped_cache_key is called. The cache key will be scoped to the model object that scoped_cache_key is invoked on, along with whatever scope is passed:

  account.scoped_cache_key(:orders)

Options: Any caching options that are passed to Rails.cache methods may be passed to scoped_cache_key. For example:

  account.scoped_cache_key(:orders, expires_in: 10.minutes)

The key that is returned can be treated as a "base key," that is, concatenated with other strings to form other cache keys. All such cache keys will become unreachable, and thus "expired," when expire_scoped_cache_key is called.

expire_scoped_cache_key

The expire_scoped_cache_key method will expire a scoped cache key obtained with scoped_cache_key. Example:

  account.expire_scoped_cache_key(:orders)

Options: The optional delay parameter specifies an amount of time to delay before actually expiring the scoped cache key. Example:

  account.expire_scoped_cache_key(:orders, delay: 5.seconds)

The delay parameter can be useful for contending with database replication lag. When many concurrent processes access the scoped cache entries, one or more may immediately try to rebuild the cache the instant that expire_scoped_cache_key completes. This could happen so quickly that the database replicas may not be caught up with the model changes that were just committed. Alternately, one could force the models to be queried from the primary database to avoid such race conditions.

The expiration delay may also be set at a global level:

    ScopedCacheKeys.expire_scoped_cache_key_delay = 10.seconds

Example

    <% cache user.scoped_cache_key :products do %>
      ... user.products.each ...
    <% end %>

    <% cache "something-else-" + user.scoped_cache_key(:products) do %>
      ... will also be expired ...
    <% end %>

    # app/sweepers/product_sweeper.rb
    class ProductSweeper < ActionController::Caching::Sweeper
      observe Product

      def after_save(record)
        record.user.expire_scoped_cache_key :products
      end
    end

Author

Zendesk
michael@grosser.it
License: MIT