AtomicRedisCache

AtomicRedisCache is an overlay on top of the redis-rb library that allows you to use Redis much like the Rails cache (ActiveSupport::Cache). It duplicates only the .fetch() method, which reads from a key if present and valid, or else evaluates the passed block and saves it as the new value at that key. The foremost design goals apply mainly to webapps and are twofold:

  • when cache expires, to avoid dogpile/thundering herd from multiple processes recalculating by serving the cached value to all but one process, then updating atomically when calculation by that process completes
  • when calculation takes too long (i.e., due to db, network calls) and a recently expired cached value is available, to fail fast with it and try calculating again later (for a reaosnable # of retries)

Installation

Add this line to your application's Gemfile:

gem 'atomic_redis_cache'

And then execute:

$ bundle

Or install it yourself as:

$ gem install atomic_redis_cache

Usage

Ensure that you set the value of AtomicRedisCache.redis. This can be either an instance of redis-rb (or compatible), or a lambda/Proc evaluating to one. Ex.

AtomicRedisCache.redis = Redis.new(:host => '127.0.0.1', :port => 6379)

Then use it as you would Rails.cache:

>> v = AtomicRedisCache.fetch('key') { Faraday.get('example.com').status }
=> 200  # network call made
>> v = AtomicRedisCache.fetch('key') { }
=> 200  # value read from cache

There are a couple of configurable options can be set per fetch:

  • :expires_in - expiry in seconds; defaults to a day
  • :race_condition_ttl - time to lock down key for recalculation
  • :max_retries - # of times to retry cache refresh before expiring

Contributing

  1. Fork it ( https://github.com/anujdas/atomic_redis_cache/fork )
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create a new Pull Request