Redis In-Memory Data Store

Redis (Remote Dictionary Server) is a free and open-source in-memory data structure store, used as a database, cache, message broker, and streaming engine. Created by Salvatore Sanfilippo (antirez) in 2009 and currently maintained by the Redis community and Redis Inc. (formerly Redis Labs), Redis is one of the most popular databases worldwide, consistently ranked in the top 10 of the DB-Engines database popularity ranking. Key features: data structures: Redis goes beyond simple key-value storage, providing rich data structures: Strings (binary-safe, up to 512 MB), Lists (linked lists), Sets (collections of unique elements), Sorted Sets (sets with floating-point scores for ranking), Hashes (field-value maps), Bitmaps, HyperLogLog (probabilistic cardinality estimation), Geospatial indexes (for location-based queries), and Streams (append-only log for messaging). Persistence: supports both RDB (point-in-time snapshots) and AOF (Append-Only File) persistence, configurable independently or together. Replication: master-replica asynchronous replication for read scaling and high availability. Redis Sentinel provides automatic failover, monitoring, and notification. Redis Cluster: built-in sharding and high-availability mode that automatically partitions data across multiple nodes (up to 1000 nodes) with automatic failover. Pub/Sub: publish-subscribe messaging pattern for real-time message broadcasting. Lua scripting: server-side Lua scripting via EVAL for atomic, complex operations. Modules: extensible module system (RedisJSON, RediSearch, RedisGraph, RedisTimeSeries, RedisBloom) for specialized data types and operations. Transactions: MULTI/EXEC commands for command grouping with optimistic locking via WATCH. Client libraries: available for virtually every programming language. Pipelining for batching commands. Cross-platform: Linux, macOS, Windows (via WSL). Redis Source Available License (RSALv2) and SSPLv1 since version 7.4.