Using Memcached Version in Ruby (Detailed Guide w/ Code Examples)

Use Case(s)

Memcached is a general-purpose distributed memory caching system often used to speed up dynamic database-driven websites by caching data and objects in RAM. The use cases in Ruby are:

1. Caching expensive queries: When you have a resource-intensive query that doesn't change often, you can cache the result.
2. Session store: Store user sessions in memcached.

Code Examples

Here's how you can set up and use Memcached with Dalli gem in Ruby:

Firstly, install the Dalli gem:

gem install dalli

Next, create an instance of the Dalli client:

client = Dalli::Client.new('localhost:11211')

You can then use this instance to interact with your Memcached server. Here's how you can store or retrieve a value:

# Set a value
client.set('key', 'value')

# Get a value
result = client.get('key')

To check the version of memcached you're running, you could use the following command:

version = client.version # => { "127.0.0.1:11211" => "1.4.37" }

The version method returns a hash where each key is the server address and the value is the server version.

Best Practices

1. Don't use Memcached as a permanent data store. It's meant for caching, which means it's okay if some items disappear occasionally.
2. Cache invalidation is one of the hardest parts in caching. Make sure to invalidate (clear) the cache when the data changes.
3. Be aware of the size of items stored in Memcached. Large objects may need to be broken down or stored elsewhere.

Common Mistakes

1. Not monitoring the Memcached servers: It's crucial to monitor hit-rates, evictions, and usage to ensure that Memcached is improving your application's performance.
2. Storing important data in Memcached: Memcached is a cache. Data can disappear due to memory pressure.

FAQs

Q: Is Memcached only useful for websites?

A: No, Memcached is valuable for caching results of any expensive computation or common database reads in any software system.

Q: Can I use Memcached as a session store?

A: Yes, but you should be aware that items can be evicted from the cache when it fills up.