Rails 4 Simple Model Caching With Redis - ruby

Question

I am new to Redis and Rails caching, and would like to perform simple model caching. I have just read these 2 articles :
http://www.sitepoint.com/rails-model-caching-redis/
http://www.victorareba.com/tutorials/speed-your-rails-app-with-model-caching-using-redis
Since Redis model caching consists in storing JSON strings in redis and retrieving them with code like
def fetch_snippets
snippets = $redis.get("snippets")
if snippets.nil?
snippets = Snippet.all.to_json
$redis.set("snippets", snippets)
end
#snippets = JSON.load snippets
end
I don't understand what is the need of using
gem 'redis-rails'
gem 'redis-rack-cache'
I don't see where the cache store or other caching mechanisms are at use in that kind of examples, since they consist only in reading/writing to Redis.
Thank you for any help.

Answer 1

Here is what I have in my Gemfile
gem 'redis'
gem 'readthis'
gem 'hiredis'
gem 'redis-browser'
readthis - recently implemented nice feature to not crash Rails when Redis is down Disable Rails caching if Redis is down. And it supports advanced Redis data types (not just strings as redis-rails).
hiredis - is a little faster
redis-browser - allows me to see what is actually cached (easier than cli).
Here is my application.rb
config.cache_store = :readthis_store, { expires_in: 1.hour.to_i, namespace: 'foobar', redis: { host: config.redis_host, port: 6379, db: 0 }, driver: :hiredis }
Then in my models I do:
def my_method_name
Rails.cache.fetch("#{cache_key}/#{__method__}", expires_in: 1.hour) do
# put my code here
end
end
I used https://github.com/MiniProfiler/rack-mini-profiler to see which queries were firing lots of DB request and determined what I should cache.

Answer 2

The snippet you posted isn't really clever. It assumes that the entire snippet collection is never updated locally, as it doesn't set any expiration for the content that is stored into Redis.
As for the gems, you don't need them at all if your goal is the example you posted.
The redis-rails is likely a plugin to connect to Redis in Rails. However, connecting to Redis is as easy as creating an initializer file and opening a new connection to Redis with the correct Redis URL using the Ruby Redis gem.
The second gem seems to add a Redis-based storage for Rack cache. If you don't know what it is, it's probably better if you don't use it at all.