Memcached (pronounced variously /mɛmkæʃˈdiː/ mem-cash-dee or /ˈmɛmkæʃt/ mem-cashed) is a general-purpose distributed memory-caching system.

[2] Memcached runs on Unix-like operating systems (Linux and macOS) and on Microsoft Windows.

Memcached's APIs provide a very large hash table distributed across multiple machines.

When the table is full, subsequent inserts cause older data to be purged in least recently used (LRU) order.

[7] Memcached is now used by many other systems, including YouTube,[8] Reddit,[9] Facebook,[10][11] Pinterest,[12][13] Twitter,[14] Wikipedia,[15] and Method Studios.

Other databases, such as MemcacheDB, Couchbase Server, provide persistent storage while maintaining Memcached protocol compatibility.

A presentation at BlackHat USA 2010 revealed that a number of large public websites had left Memcached open to inspection, analysis, retrieval, and modification of data.

Some attempt to isolate setting and reading data may be made in situations such as high volume web publishing.

In February 2018, CloudFlare reported that misconfigured memcached servers were used to launch DDoS attacks in large scale.

[23] Victims of the DDoS attacks include GitHub, which was flooded with 1.35 Tbit/s peak incoming traffic.

If the result does not exist, it would select from the database as usual, and set the unique key using the Memcached API add function call.

Similar action would need to be taken when database records were deleted, to maintain either a correct or incomplete cache.