SyncedMemoryStore

An active support cache store that can be synced across processes using redis.

The use case for this gem is to work alongside a rails cache for 'high priority' entries that should stay in sync across all processes using the shared cache.

So, imagine you had 10 web processes all asking for a logged in user or an access key from the database. If you were to cache this in memory normally and changed a user or access key in one process - the cache would then be stale in the other 9. So, you could use a memcache based cache or redis based - but then you are hitting memcache or redis on every request for something that doesnt change often.

SyncedMemoryStore to the rescue

It is an in memory cache in front of a secondary cache for persistence. But the in memory cache is synced using redis - so as long as your REDIS_URL environment variable is set to the same URL - or you can configure your own redis adapter - then it will just work.

Installation

Add this line to your application's Gemfile:

gem 'synced_memory_store'

And then execute:

$ bundle

Or install it yourself as:

$ gem install synced_memory_store

Usage

In an irb console in terminal window 1

    persistent_cache = ActiveSupport::Cache::RedisStore.new(ENV.fetch('REDIS_URL'))
    cache = SyncedMemoryStore::Store.new(cache: cache_1, redis: redis)

In an irb console in terminal window 2

    persistent_cache = ActiveSupport::Cache::RedisStore.new(ENV.fetch('REDIS_URL'))
    cache = SyncedMemoryStore::Store.new(cache: cache_1, redis: redis)

Then, to write a value to the cache in terminal window 1

    cache.write("key", "it works")

Then, check it in terminal window 2

    cache.fetch("key")
    >> "it works"

And it has done this without querying the persistent cache - you can prove this by replacing the RedisStore with a MemoryStore.

See the specs for more details

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.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/[USERNAME]/synced_memory_store.

License

The gem is available as open source under the terms of the MIT License.