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

Use Case(s)

The incr command in Memcached is used to atomically increment a key's value. This is particularly useful in scenarios where you need to track counts or other numeric stats that might be frequently updated and accessed concurrently. Examples could include tracking page views, user votes, or any other counters.

Code Examples

Let's assume we have a Memcached instance up and running on localhost, port 11211. We'll use the 'dalli' gem, a popular Ruby client for Memcached.

Firstly, ensure you have dalli added to your Gemfile:

gem 'dalli'

Now install it using Bundler:

bundle install

To use incr function:

require 'dalli' # Create a client instance client ='localhost:11211') # Set an initial value for our key client.set('counter', 0) # Now we can increment our counter client.incr('counter', 1) # It should now return 1 puts client.get('counter') # outputs: 1 # If you increment again client.incr('counter', 1) # It should now return 2 puts client.get('counter') # outputs: 2

In this example, we first set an initial value for our key 'counter'. Then we increment it by 1 twice, and each time we get the incremented value back.

Best Practices

  • Always initialize keys before you try to increment them, since Memcached's incr operation only works when the key already exists.
  • Think about failure scenarios. What if Memcached goes down or the network connection is lost? Depending on how crucial the data is, you may need a strategy to handle such situations.

Common Mistakes

  • Using incr on non-numeric values. The incr operation only works with numeric values.
  • Expecting incr to initialize a key if it does not exist; instead, it will just return nil.


Q: What happens if I try to increment a key that doesn't exist? A: Memcached's incr method will return nil if it cannot find the key.

Q: What happens if I use incr on a key with string value? A: The incr method should only be used on keys with numeric values. If you try to increment a key associated with a string or non-numeric value, it won't work, and it might lead to unexpected behavior.

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