- cache:
memcached - Persistent Storage solution：
dbcached = memcached + nmdb
nmdb = nmdb(memcached) => QDBM/berkeley db
memcachedb = memcached(protocol) => berkeley db
TokyoTyrant = memcached(protocol) => TokyoCabinet - dbm：
TokyoCabinet(successor of QDBM)
QDBM
berkeley db