Redis

Redis is an open-source, in-memory data store used as a database, cache, streaming engine, and message broker. Redis is open source under the BSD license and is capable of delivering sub-millisecond response times to enable millions of requests per second for real-time applications.

Redis provides data structures, such as strings, hashes, lists, sets, sorted sets with range queries, bitmaps, hyperloglogs, geospatial indexes, and streams. It has built-in replication, Lua scripting, LRU eviction, transactions, and different levels of on-disk persistence. And depending on the use case, Redis can persist data either by periodically dumping the dataset to disk or by appending each command to a disk-based log.

Further, Redis is developed to allow users to run atomic operations, like appending to a string, incrementing the value in a hash, pushing an element to a list, computing set intersection, union and difference, or ranking members in a sorted list. Redis also supports asynchronous replication with non-blocking synchronization and auto-reconnection with partial resynchronization on net spill.