OStatic

memcached is a general-purpose distributed memory caching system that was originally developed by Danga Interactive for LiveJournal, but is now used by many other sites. It is often used to speed up dynamic database-driven websites by caching data and objects in memory to reduce the number of times the database must be read. Memcached is distributed under a permissive free software licence.

Memcached lacks authentication and security features, meaning it should only be used on servers with a firewall set up appropriately. By default, memcached uses the port 11211. Among other technologies, it uses libevent.

Memcached's APIs provide a giant 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. Applications using memcached typically layer memcached requests and additions into code before falling back on a slower backing store, such as a database.

The system is used by several very large, well-known sites including YouTube[, LiveJournal, Slashdot, Wikipedia, SourceForge, GameFAQs, Facebook, Digg, Fotolog, BoardGameGeek, deviantART and Kayak.