|Initial release||April 10, 2009|
3.2.4 / September 26, 2016
|Written in||ANSI C|
|Type||Data structure store|
The name Redis means REmote DIctionary Server. Salvatore Sanfilippo, the original developer of Redis, was hired by VMware in March, 2010. In May, 2013, it was sponsored by Pivotal Software (a VMware spin-off). In June 2015, development became sponsored by Redis Labs.
According to monthly rankings by DB-Engines.com, Redis is often ranked the most popular key-value database. Redis has also been ranked the #4 NoSQL database in user satisfaction and market presence based on user reviews, the most popular NoSQL database in containers, and the #1 NoSQL database among Top 50 Developer Tools & Services.
- Lists of strings
- Sets of strings (collections of non-repeating unsorted elements)
- Sorted sets of strings (collections of non-repeating elements ordered by a floating-point number called score)
- Hash tables where keys and values are strings
- HyperLogLogs used for approximated set cardinality size estimation.
The type of a value determines what operations (called commands) are available for the value itself. Redis supports high-level, atomic, server-side operations like intersection, union, and difference between sets and sorting of lists, sets and sorted sets.
Redis typically holds the whole dataset in memory. Versions up to 2.4 could be configured to use what they refer to as virtual memory in which some of the dataset is stored on disk, but this feature is deprecated. Persistence is now achieved in two different ways: one is called snapshotting, and is a semi-persistent durability mode where the dataset is asynchronously transferred from memory to disk from time to time, written in RDB dump format. Since version 1.1 the safer alternative is AOF, an append-only file (a journal) that is written as operations modifying the dataset in memory are processed. Redis is able to rewrite the append-only file in the background in order to avoid an indefinite growth of the journal.
By default, Redis writes data to a file system at least every 2 seconds, with more or less robust options available if needed. In the case of a complete system failure on default settings, only a few seconds of data would be lost.
Redis supports master-slave replication. Data from any Redis server can replicate to any number of slaves. A slave may be a master to another slave. This allows Redis to implement a single-rooted replication tree. Redis slaves can be configured to accept writes, permitting intentional and unintentional inconsistency between instances. The Publish/Subscribe feature is fully implemented, so a client of a slave may SUBSCRIBE to a channel and receive a full feed of messages PUBLISHed to the master, anywhere up the replication tree. Replication is useful for read (but not write) scalability or data redundancy.
When the durability of data is not needed, the in-memory nature of Redis allows it to perform well compared to database systems that write every change to disk before considering a transaction committed. Redis operates as a single process and is single-threaded. Therefore, a single Redis instance cannot utilize parallel execution of tasks such as stored procedures (Lua scripts).
The Redis project has a cluster specification, According to a news post by Redis creator Sanfilippo, the first production version of Redis cluster (planned for beta release at end of 2013),[needs update?] was supposed to support automatic partitioning of the key space and hot resharding, but will support only single key operations. In the future Redis Cluster is planned to support up to 1000 nodes, fault tolerance with heartbeat and failure detection, incremental versioning ("epochs") to prevent conflicts, slave election and promotion to master, and publish/subscribe between all cluster nodes.
- An interview with Salvatore Sanfilippo, creator of Redis, working out of Sicily, January 4, 2011, by Stefano Bernardi, EU-Startups
- Salvatore Sanfilippo – Welcome to Redis Labs, July 15, 2015, By Itamar Haber, Redis Labs
- "Redis release notes".
- "FAQ, Redis".
- Gwen Shapira (March 17, 2010). "VMware Hires Redis Key Developer – But Why?". Blog. Retrieved September 25, 2016.
- Salvatore Sanfilippo (March 15, 2010). "VMware: the new Redis home". Blog. Retrieved September 25, 2016.
- Derek Collison (March 15, 2010). "VMware: The Console: VMware hires key developer for Redis". Blog. Archived from the original on March 22, 2010. Retrieved September 25, 2016.
- Salvatore Sanfilippo. "Redis Sponsors". Redis Labs. Retrieved September 25, 2016.
- Thanks Pivotal, Hello Redis Labs, July 15, 2015, By Salvatore Sanfilippo, Redis Labs
- DB-Engines Ranking of Key-value Stores
- Best NoSQL Databases: Fall 2015 Report from G2 Crowd
- The Current State of Container Usage
- Top 50 Developer Tools and Services of 2015
- Redis language bindings
- CRAN – Package rredis
- Redis documentation "Virtual Memory", redis.io, accessed January 18, 2011.
- ReplicationHowto – redis – A persistent key-value database with built-in net interface written in ANSI-C for Posix systems – Google Project Hosting
- Redis Cluster Specification, Redis.io, Retrieved 2013-12-25.
- Redis Download Page, Redis.io, Retrieved 2013-12-25.
- News about Redis: 2.8 is shaping, I'm back on Cluster, Antirez Weblog - Salvatore Sanfilippo, Retrieved 2013-12-25.
- Redis Cluster - a Pragmatic Approach to Distribution, Redis.io, Retrieved 2013-12-25.
- Further reading
- Jeremy Zawodny, Redis: Lightweight key/value Store That Goes the Extra Mile, Linux Magazine, August 31, 2009
- Isabel Drost and Jan Lehnard (29 October 2009), Happenings: NoSQL Conference, Berlin, The H. Slides for the Redis presentation. Summary.
- Billy Newport (IBM): "Evolving the Key/Value Programming Model to a Higher Level" Qcon Conference 2009 San Francisco.
- A Mishra: "Install and configure Redis on Centos/ Fedora server".
- E. Mouzakitis: "Monitoring Redis Performance"