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This article is about Redis software. For Redis people, see Romani people.
Redis Logo.svg
Developer(s) Salvatore Sanfilippo[1][2]
Initial release April 10, 2009; 7 years ago (2009-04-10)
Stable release
3.2.4 / September 26, 2016; 23 days ago (2016-09-26)[3]
Development status Active
Written in ANSI C
Operating system Cross-platform
Available in English
Type Data structure store
License BSD

Redis is a software project that implements data structure servers. It is open-source, networked, in-memory, and stores keys with optional durability.


The name Redis means REmote DIctionary Server.[4] Salvatore Sanfilippo, the original developer of Redis, was hired by VMware in March, 2010.[5][6][7] In May, 2013, it was sponsored by Pivotal Software (a VMware spin-off).[8] In June 2015, development became sponsored by Redis Labs.[9]

According to monthly rankings by, Redis is often ranked the most popular key-value database.[10] Redis has also been ranked the #4 NoSQL database in user satisfaction and market presence based on user reviews,[11] the most popular NoSQL database in containers,[12] and the #1 NoSQL database among Top 50 Developer Tools & Services.[13]

Supported languages[edit]

Many languages have Redis bindings, including:[14] ActionScript, C, C++, C#, Chicken Scheme, Clojure, Common Lisp, D, Dart, Erlang, Go, Haskell, Haxe, Io, Java, JavaScript (Node.js), Julia, Lua, Objective-C, OCaml, Perl, PHP, Pure Data, Python, R,[15] Racket, Ruby, Rust, Scala, Smalltalk and Tcl.

Data types[edit]

Redis maps keys to types of values. A key difference between Redis and other structured storage systems is that Redis supports not only strings, but also abstract data types:

  • 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[16] 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.[17]


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.[4] 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,[18] According to a news post by Redis creator Sanfilippo, the first production version of Redis cluster (planned for beta release at end of 2013),[19][needs update?] was supposed to support automatic partitioning of the key space and hot resharding, but will support only single key operations.[20] 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.[18][21]

See also[edit]


  1. ^ An interview with Salvatore Sanfilippo, creator of Redis, working out of Sicily, January 4, 2011, by Stefano Bernardi, EU-Startups
  2. ^ Salvatore Sanfilippo – Welcome to Redis Labs, July 15, 2015, By Itamar Haber, Redis Labs
  3. ^ "Redis release notes". 
  4. ^ a b "FAQ, Redis". 
  5. ^ Gwen Shapira (March 17, 2010). "VMware Hires Redis Key Developer – But Why?". Blog. Retrieved September 25, 2016. 
  6. ^ Salvatore Sanfilippo (March 15, 2010). "VMware: the new Redis home". Blog. Retrieved September 25, 2016. 
  7. ^ 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. 
  8. ^ Salvatore Sanfilippo. "Redis Sponsors". Redis Labs. Retrieved September 25, 2016. 
  9. ^ Thanks Pivotal, Hello Redis Labs, July 15, 2015, By Salvatore Sanfilippo, Redis Labs
  10. ^ DB-Engines Ranking of Key-value Stores
  11. ^ Best NoSQL Databases: Fall 2015 Report from G2 Crowd
  12. ^ The Current State of Container Usage
  13. ^ Top 50 Developer Tools and Services of 2015
  14. ^ Redis language bindings
  15. ^ CRAN – Package rredis
  16. ^ Redis documentation "Virtual Memory",, accessed January 18, 2011.
  17. ^ ReplicationHowto – redis – A persistent key-value database with built-in net interface written in ANSI-C for Posix systems – Google Project Hosting
  18. ^ a b Redis Cluster Specification,, Retrieved 2013-12-25.
  19. ^ Redis Download Page,, Retrieved 2013-12-25.
  20. ^ News about Redis: 2.8 is shaping, I'm back on Cluster, Antirez Weblog - Salvatore Sanfilippo, Retrieved 2013-12-25.
  21. ^ Redis Cluster - a Pragmatic Approach to Distribution,, Retrieved 2013-12-25.
Further reading

External links[edit]