atomic_cache Gem

User Documentation

• Installation & Project Setup
• Model Setup
• Usage & Testing
• Custom Clients/Adapters

atomic_cache is a gem which prevents the thundering herd problem

In a nutshell:

• The key of every cached value includes a timestamp
• Once a cache key is written to, it is never written over
• When a newer version of a cached value is available, it's written to a new key (e.g. same key with a newer timestamp)
• When a new value is being generated for a new key only 1 process is allowed to do so at a time
• While the new value is being generated, other processes read one key older than most recent (last known value)
• If the last known value isn't available other processes wait for the new value, polling periodically for it

Quick Reference

class Foo < ActiveRecord::Base
  include AtomicCache::GlobalLMTCacheConcern

  force_cache_class(:custom_foo)  # optional
  cache_version(5)          # optional

  def active_foos(ids)
    keyspace = cache_keyspace(:activeids, ids)
    atomic_cache.fetch(keyspace, expires_in: 5.minutes) do
      Foo.active.where(id: ids.uniq)
    end

    # value stored at 'company:custom_foo:activeids:<ids hash>:1270643035.04671'
    # last mod time stored at 'company:custom_foo:lmt'
  end
end

For further details and examples see Usage & Testing

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/ibotta/atomic_cache

Releasing

Releases are automatically handled via the Travis CI build. When a version greater than the version published on rubygems.org is pushed to the main branch, Travis will:

• re-generate the CHANGELOG file
• tag the release with GitHub
• release to rubygems.org