Question: Who decides which Memcached server to connect?

Answer

The client application decides which Memcached server to connect by specifying the IP address and port number of one or more Memcached servers.

In a typical setup, multiple Memcached servers are deployed in a cluster to ensure high availability and scalability. The client application can distribute the workload across these servers by using a consistent hashing algorithm.

Consistent hashing is a technique used by distributed systems to map keys onto nodes in a way that minimizes the amount of remapping required when nodes are added or removed from the system. In Memcached, consistent hashing is implemented by using a ring of hash values to map keys onto server nodes. Each client keeps a copy of this ring and uses it to determine the server responsible for a given key.

Here's an example Python code snippet that demonstrates how to connect to a Memcached server using the python-memcached library:

import memcache

client = memcache.Client(['127.0.0.1:11211'])
client.set('key', 'value')
result = client.get('key')
print(result)

In this example, the client connects to a Memcached server running on 127.0.0.1 at port 11211. The set() method is used to store a key-value pair in the cache, and the get() method is used to retrieve the value associated with the key.