Memcached Data Model (Key-Value Storage, where data is stored in key-value pairs)

Memcached is a high-performance in-memory caching system designed to provide fast and efficient data storage and retrieval services. It uses a key-value pair storage model, where data is stored as key-value pairs, enabling a simple and efficient data management mechanism.

Key-Value Model

Each data item in Memcached consists of a unique key and a corresponding value. The key can be any type of string, such as integers, floating-point numbers, or strings. However, for Memcached, it is best to use ASCII strings.

Key Definition

In Memcached, keys are defined as follows:

  • KEY_MAXLEN: The maximum length allowed for storage is 1024 characters.
  • KEY_EXPIRE: The expiration time of the key, which can be set to a specific point in time or a valid duration (e.g., in seconds).
  • KEY casl: Memcached supports caslock (caslock: implementing atomic operations in a multi-threaded environment) and caslockless (no locking required). If caslock is used, data security is guaranteed.

Value Definition

Values can also be any type of string, including numbers, floating-point numbers, and strings. However, if structured data such as JSON or XML is stored, in practical applications, this data is typically stored in Memcached in a serialized form (e.g., JSON, XML). When these structured data need to be used, they can be retrieved from Memcached and parsed back into their original structure.

Memcached Read/Write Operations

Memcached provides various read/write operations, including:

  • GET: Used to retrieve a key-value pair.
  • SET: Used to set or update a key-value pair.
  • DEL: Used to delete a key-value pair.
  • INCR: Used to increment a counter value.

Memcached Data Storage Method

Memcached uses a data structure called a linked list to store its key-value pairs. In this linked list, each item is a simple structure containing a key, a value, and a pointer to the next item. This design enables Memcached to quickly retrieve and set data.

Advantages of Memcached

  • High Performance: Memcached is renowned for its high-speed data storage and retrieval.
  • Low Latency: Because Memcached uses in-memory caching, read/write speeds are extremely fast.
  • Relieves Database Load: By caching frequently queried data, the burden on the database can be reduced.

Disadvantages of Memcached

  • Data Loss: Data in Memcached is lost upon restart.
  • Memory Dependency: If Memcached runs out of memory, it may lead to data loss.