Question: How does Memcached work?

Answer

Memcached is a distributed, in-memory key-value store that is commonly used for caching data and reducing database load. It works by storing data in memory, providing fast access to frequently accessed data.

When a client requests data from Memcached, the server checks if the requested data exists in memory. If it does, the server returns the data to the client. If the data does not exist in memory, the server must retrieve the data from its persistent storage, such as a database or file system, and store it in memory before returning it to the client.

Data in Memcached is stored using a simple key-value model where data is identified by a unique key. Keys can be any string up to 250 bytes in length, and values can be any binary data up to 1MB in size. Memcached provides various commands for interacting with the data, including GET, SET, ADD, REPLACE, DELETE, and more.

To improve performance, Memcached uses a technique called "sharding" to distribute data across multiple servers. Each server stores a portion of the total data set, determined by a consistent hashing algorithm. This allows Memcached to scale horizontally by adding more servers as needed to handle increased traffic.

Here's an example of how to use Memcached with PHP:

// connect to memcached server
$memcached = new Memcached();
$memcached->addServer('localhost', 11211);

// set a value
$memcached->set('mykey', 'myvalue');

// get a value
$value = $memcached->get('mykey');
echo $value; // output: myvalue

// delete a value
$memcached->delete('mykey');

Overall, Memcached provides a simple yet powerful way to cache frequently accessed data and reduce database load, making it a popular choice for web applications that require high performance and scalability.