Redis

File:Salvatore Sanfilippo.png

The name Redis means Remote Dictionary Server. The Redis project began when Salvatore Sanfilippo, nicknamed antirez, the original developer of Redis, was trying to improve the scalability of his Italian startup, developing a real-time web log analyzer. After encountering significant problems in scaling some types of workloads using traditional database systems, Sanfilippo began in 2009 to prototype a first proof of concept version of Redis in Tcl.{{cite web |title=Tcl prototype of Redis |date=April 28, 2017 |website=GitHub Gist |last=Sanfilippo |first=Salvatore |url=https://gist.github.com/antirez/6ca04dd191bdb82aad9fb241013e88a8 |access-date=October 8, 2018}} Later Sanfilippo translated that prototype to the C language and implemented the first data type, the list. After a few weeks of using the project internally with success, Sanfilippo decided to open source it, announcing the project on Hacker News. The project began to get traction, particularly among the Ruby community, with GitHub and Instagram being among the first companies adopting it.{{cite web |title=Introducing Resque |date=November 3, 2009 |website=Blog |last=Wanstrath |first=Chris |url=https://blog.github.com/2009-11-03-introducing-resque/ |access-date=October 8, 2018}}{{cite web |url=https://instagram-engineering.com/storing-hundreds-of-millions-of-simple-key-value-pairs-in-redis-1091ae80f74c |title=Storing hundreds of millions of simple key-value pairs in Redis |date=October 31, 2011 |last=Krieger |first=Mike |website=Instagram Engineering Blog |access-date=October 8, 2018}}

Sanfilippo was hired by VMware in March 2010.{{cite web |title=VMware Hires Redis Key Developer – But Why? |date=March 17, 2010 |website=Blog |last=Shapira |first=Gwen |url=https://prodlife.wordpress.com/2010/03/17/vmware-hires-redis-key-developer-but-why/ |access-date=September 25, 2016}}{{cite web |title=VMware: the new Redis home |website=Blog |date=March 15, 2010 |last=Sanfilippo |first=Salvatore |url=http://antirez.com/post/vmware-the-new-redis-home.html |access-date=September 25, 2016}}{{cite web |url=http://blogs.vmware.com/console/2010/03/vmware-hires-key-developer-for-redis.html |title=VMware: The Console: VMware hires key developer for Redis |website=VMware Blog |date=March 15, 2010 |last=Collison |first=Derek |archive-url=https://web.archive.org/web/20100322191425/http://blogs.vmware.com/console/2010/03/vmware-hires-key-developer-for-redis.html |archive-date=March 22, 2010 |access-date=September 25, 2016 |url-status=dead }}

In May 2013, Redis was sponsored by Pivotal Software (a VMware spin-off).{{cite web |url=https://redis.io/topics/sponsors |title=Redis Sponsors |last=Sanfilippo |first=Salvatore |website=Redis.io |publisher=Redis |access-date=April 11, 2019}}

In June 2015, development became sponsored by Redis Ltd.{{Cite web |last=Sanfilippo |first=Salvatore |date=July 15, 2015 |title=Thanks Pivotal, Hello Redis Labs |url=http://antirez.com/news/91 |access-date=2019-04-03 |website=antirez.com}}

In August 2018, to control usage of the software by managed cloud providers without adequate compensation, Redis Ltd. announced that it would relicense the optional Redis modules from the GNU Affero General Public License (AGPL) to the Apache License, but subject to an addendum known as the "Commons Clause" that restricts commercial usage. This made the modules source-available and no longer free software. The core Redis software remained under a BSD license, with Redis Ltd. committing to maintaining these terms.{{Cite web |last=Baer |first=Tony |date=October 16, 2018 |title=It's MongoDB's turn to change its open source license |url=https://www.zdnet.com/article/its-mongodbs-turn-to-change-its-open-source-license/ |access-date=2019-08-01 |website=ZDNet |language=en}}{{cite web |last=Shoolman |first=Yiftach |date=August 22, 2018 |title=Redis' License is BSD and will remain BSD |url=https://redis.io/blog/redis-license-bsd-will-remain-bsd/ |access-date=September 30, 2024 |website=Redis.io |publisher=Redis}}

In October 2018, Redis 5.0 was released, introducing Redis Stream – a new data structure that allows storage of multiple fields and string values with an automatic, time-based sequence at a single key.{{Cite web|url=https://redis.com/blog/redis-5-0-is-here/|title = Redis 5.0 is here!|date = 22 October 2018}}

In February 2019, citing confusion over the licensing terms, the Apache License with Commons Clause licensing terms for Redis modules was replaced with the "Redis Source Available License" (RSAL), which explicitly prohibits commercial use of the modules as part of "a database, a caching engine, a stream processing engine, a search engine, an indexing engine or an ML/DL/AI serving engine."{{Cite magazine |last=Finley |first=Klint |date=July 31, 2019 |title=When Open Source Software Comes With a Few Catches |url=https://www.wired.com/story/when-open-source-software-comes-with-catches/ |access-date=2019-08-01 |magazine=Wired |language=en |issn=1059-1028}}{{Cite web |last=Vaughan-Nichols |first=Steven J. |title=Redis Labs drops Commons Clause for a new license |url=https://www.zdnet.com/article/redis-labs-drops-commons-clause-for-a-new-license/ |access-date=2019-08-01 |website=ZDNet |language=en}} The last revision of the modules under a free and open source license were forked by community members as the GoodFORM project.{{Cite web |last=Gilbertson |first=Scott |date=2019-10-16 |title=In 2019, multiple open source companies changed course—is it the right move? |url=https://arstechnica.com/information-technology/2019/10/is-the-software-world-taking-too-much-from-the-open-source-community/ |access-date=2019-10-16 |website=Ars Technica |language=en-us}}

In June 2020, Salvatore Sanfilippo stepped down as Redis' sole maintainer. Sanfilippo was succeeded by Yossi Gottlieb and Oran Agra.{{Cite web |title=The end of the Redis adventure - |url=http://antirez.com/news/133 |access-date=2020-11-10 |website=antirez.com}}

In March 2024, Redis Ltd. announced that beginning with version 7.4, the core Redis software would be relicensed under the RSAL and Server Side Public License (SSPL), both of which are source-available and non-free.{{Cite news |title=Redis tightens its license terms, pleasing no one |url=https://www.theregister.com/2024/03/22/redis_changes_license/ |archive-url=http://web.archive.org/web/20250206143748/https://www.theregister.com/2024/03/22/redis_changes_license/ |archive-date=2025-02-06 |access-date=2025-05-01 |work=The Register |language=en}} The Linux Foundation subsequently announced that it would fork the last BSD-licensed version of Redis as Valkey.{{Cite web |title=Linux Foundation Launches Valkey As A Redis Fork |url=https://www.phoronix.com/news/Linux-Foundation-Valkey |access-date=2025-05-01 |website=Phoronix |language=en}} In May 2025, Redis Ltd. announced that it would change the license again to the AGPL beginning on version 8.0, citing that that forks had achieved their goal of creating a "level playing field" of differentiated products, and that Redis has achieved "record growth" since the change in license.{{Cite web |title=Redis bets big on an open source return |url=https://www.infoworld.com/article/3975620/redis-bets-big-on-an-open-source-return.html |access-date=2025-05-01 |website=InfoWorld |language=en-US}}

Redis popularized the idea of a system that can be considered a store and a cache at the same time. It was designed so that data is always modified and read from the main computer memory, but also stored on disk in a format that is unsuitable for random data access. The formatted data is only reconstructed into memory once the system restarts.

Redis also provides a data model that is very unusual compared to a relational database management system (RDBMS). User commands do not describe a query to be executed by the database engine but rather specific operations that are performed on given abstract data types. Therefore data must be stored in a way which is suitable later for fast retrieval. The retrieval is done without help from the database system in form of secondary indexes, aggregations or other common features of traditional RDBMS. The Redis implementation makes heavy use of the fork system call, to duplicate the process holding the data, so that the parent process continues to serve clients while the child process writes the in-memory data to disk.

According to monthly DB-Engines rankings, Redis is often the most popular key–value database.{{cite web |url=http://db-engines.com/en/ranking/key-value+store |title=DB-Engines Ranking - popularity ranking of key-value stores |website=DB-Engines}} Redis has also been ranked the #4 NoSQL database in user satisfaction and market presence based on user reviews,{{cite web |url=http://about.g2crowd.com/press-release/best-nosql-databases-fall-2015/ |title=Best NoSQL Databases: Fall 2015 Report from G2 Crowd |publisher=G2 Crowd |access-date=2015-08-25 |archive-date=2015-08-24 |archive-url=https://web.archive.org/web/20150824012237/http://about.g2crowd.com/press-release/best-nosql-databases-fall-2015/ |url-status=dead }} the most popular NoSQL database in containers,{{cite web |url=https://www.datadoghq.com/docker-adoption/ |title=8 Surprising Facts about Real Docker Adoption |website=Datadog|date=13 June 2018 }} and the #4 Data store of 2019 by ranking website stackshare.io.{{Cite web|title=🏆 The Top 50 Developer Tools of 2019|url=https://stackshare.io/posts/top-developer-tools-2019|access-date=2020-07-28|website=StackShare|language=en}} It was voted most loved database in the Stack Overflow [https://insights.stackoverflow.com/survey/ Developer Survey] each year from 2017 to 2021,{{cite web|url=https://insights.stackoverflow.com/survey/2021#section-most-loved-dreaded-and-wanted-databases|title=Developer Survey Results 2021: Most Loved, Dreaded, and Wanted Databases|website=Stack Overflow|publisher=Stack Exchange|access-date=2021-08-23}} however, it has since fallen to sixth place.{{cite web|url=https://survey.stackoverflow.co/2024/technology#most-popular-technologies-database|title=2024 Stack Overflow Developer Survey|website=Stack Overflow|publisher=Stack Exchange|access-date=2025-04-24}}

Since version 2.6, Redis features server-side scripting in the language Lua.{{cite web |url=https://redis.io/commands/eval |title=EVAL – Redis |website=redis.io}}

Many programming languages have Redis language bindings on the client side, including:{{cite web |url=https://redis.io/clients |title=Redis |website=redis.io}} ActionScript, C, C++, C#, Chicken, Clojure, Common Lisp, Crystal, D, Dart, Delphi,{{cite web | url=https://github.com/danieleteti/delphiredisclient | title=Danieleteti/Delphiredisclient | website=GitHub | date=17 September 2022 }} Elixir, Erlang, Go, Haskell, Haxe, Io, Java, Nim, JavaScript (Node.js), Julia, Lua, Objective-C, OCaml, Perl, PHP, Pure Data, Python, R,{{cite web |url=https://cran.r-project.org/web/packages/rredis/ |title=rredis: "Redis" Key/Value Database Client |last=Lewis |first=B. W. |date=5 July 2015 |website=The Comprehensive R Archive Network |access-date=2019-04-03}} Racket, Ruby, Rust, Scala, Smalltalk, Swift, and Tcl. Several client software programs exist in these languages.

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

• [https://redis.io/docs/latest/develop/data-types/strings String] - A Redis string is the most basic Redis data type. It holds a sequence of bytes. A string may represent a text, an integer value, a floating-point value, a serialized object, or anything else.

• [https://redis.io/docs/latest/develop/data-types/json/#use-redisjson JSON] - The Redis JSON data type provides JavaScript Object Notation (JSON) support for Redis. It lets users store, retrieve, and update JSON documents. A JSON document can be queried and manipulated using JSONPath expressions. JSON works seamlessly with the Redis Query Engine to let users index and query JSON documents.

• [https://redis.io/docs/latest/develop/data-types/hashes Hash] A Redis hash is a collection of fields, each field is a name-value string pair. Users can use hashes to represent flat objects and to store groupings of counters, among other things. Expiration time or a time-to-live can be set for each hash field. Hash works seamlessly with the Redis Query Engine to let users index and query hashes.

• [https://redis.io/docs/latest/develop/interact/search-and-query/ Redis Query Engine] The Redis Query Engine allows users to use Redis as a document database, a vector database, a secondary index, and a search engine. With Redis Query Engine, users can define indexes for hash and JSON documents, and use a rich query language for vector search, full-text search, geospatial queries, and aggregations.

• [https://redis.io/docs/latest/develop/data-types/lists List] A Redis list is a list of strings, sorted by insertion order. Lists are great for stacks, queues, and for queue management and worker systems.

• [https://redis.io/docs/latest/develop/data-types/sets Set] A Redis set is an unordered collection of unique strings (members). Sets can be used to track unique items (e.g., track all unique IP addresses accessing a given blog post), represent relations (e.g., the set of all users with a given role). Redis also supports common set operations such as intersection, union, and difference.

• [https://redis.io/docs/latest/develop/data-types/sorted-sets Sorted Set] A Redis sorted set is similar to a set, but each member is associated with a score. When more than one member has the same score, the members are ordered lexicographically. Some use cases for sorted sets include leaderboards and sliding-window rate limiters.

• [https://redis.io/docs/latest/develop/data-types/vector-sets Vector Set] A Redis vector set is a data type similar to a sorted set, but instead of a score, each member is associated with a vector embedding. Users can add items to a vector set and then retrieve the members that are the most similar to a specified vector embedding or the vector embedding of an existing member.

• [https://redis.io/docs/latest/develop/data-types/geospatial/ Geospatial Index] Redis Geospatial indexes let users store coordinates and search for them. This data structure is useful for finding nearby points within a given radius or bounding box.

• [https://redis.io/docs/latest/develop/data-types/bitmaps/ Bitmap] Redis bitmaps provide bit-oriented operations on a bit array. Users can get bits, set bits, and perform bitwise operations between bitmaps. Bitmaps are often used to efficiently manage memberships or permissions, where each bit represents a particular member.

• [https://redis.io/docs/latest/develop/data-types/bitfields/ Bitfield] Redis bitfields let users set, increment, and get integer values of arbitrary bit length - from unsigned 1-bit integers to signed 63-bit integers. Bitfields are often used to efficiently manage arrays of limited-range counters or numerical values.

• [https://redis.io/docs/latest/develop/data-types/hyperloglogs HyperLogLog] Redis HyperLogLog is a Redis probabilistic data structure used for approximating the cardinality of a stream (i.e., the number of unique elements).

• [https://redis.io/docs/latest/develop/data-types/probabilistic/bloom-filter/ Bloom filter] Bloom filter is a Redis probabilistic data structure used for checking if a given value is present in a stream.

• [https://redis.io/docs/latest/develop/data-types/probabilistic/cuckoo-filter/ Cuckoo filter] Cuckoo filter, just like Bloom filter, is a Redis probabilistic data structure for checking if a given value is present in a stream, while also allowing limited counting and deletions.

• [https://redis.io/docs/latest/develop/data-types/probabilistic/top-k/ Top-k] Top-k is a Redis probabilistic data structure used for tracking the most frequent values in a stream.

• [https://redis.io/docs/latest/develop/data-types/probabilistic/count-min-sketch/ Count-min sketch] Count–min sketch is a Redis probabilistic data structure used for estimating how many times a given value appears in a stream.

• [https://redis.io/docs/latest/develop/data-types/probabilistic/t-digest/ t-digest] t-digest is a Redis probabilistic data structure used for estimating which fraction / how many values in a stream are smaller than a given value, or which value is smaller than p percent of the values in a stream (the p-percentile value).

• [https://redis.io/docs/latest/develop/data-types/timeseries/quickstart/ Time Series] A Redis time series allows storing and querying a series of timetagged data points (samples).

• [https://redis.io/docs/latest/develop/interact/pubsub/ Pub/Sub] Redis Pub/Sub (short for publish/subscribe) is a lightweight messaging capability. Publishers send messages to a channel, and subscribers receive messages from that channel.

• [https://redis.io/docs/latest/develop/data-types/streams/ Stream] A Redis stream is a data structure that acts like an append-only log. Each stream entry consists of name-value string pairs, similar to a hash. Streams support multiple consumption strategies, where consumers can pop entries, consume entries by range, or listen to entries. Consumer groups allow multiple workers to retrieve different stream entries in order to scale message processing.

• [https://redis.io/docs/latest/develop/interact/transactions/ Transactions] A Redis transaction allows the execution of a group of commands in a single step. A request sent by another client will never be served during the execution of a transaction. This guarantees that the commands are executed as a single isolated operation.

• [https://redis.io/docs/latest/develop/interact/programmability/eval-intro/ Programmability] Redis users can upload and execute Lua scripts on the server. Scripts can employ programmatic control structures and use most of the commands while executing to access the database. Because scripts are executed on the server, reading and writing data from scripts is very efficient. Functions provide the same core functionality as scripts but are first-class software artifacts of the database. Redis manages [https://redis.io/docs/latest/develop/interact/programmability/functions-intro/ functions] as an integral part of the database and ensures their availability via data persistence and replication.

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{{cite web |url=https://redis.io/topics/virtual-memory |title=Virtual Memory |website=Redis.io |access-date=April 11, 2019}} in which some of the dataset is stored on disk, but this feature is deprecated. Persistence in Redis can be achieved through two different methods. First by snapshotting, where the dataset is asynchronously transferred from memory to disk at regular intervals as a binary dump, using the Redis RDB Dump File Format. Alternatively by journaling, where a record of each operation that modifies the dataset is added to an append-only file (AOF) in a background process. Redis can rewrite the append-only file in the background to avoid an indefinite growth of the journal. Journaling was introduced in version 1.1 and is generally considered the safer approach.

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–replica replication. Data from any Redis server can replicate to any number of replicas. A replica may be a master to another replica. This allows Redis to implement a single-rooted replication tree. Redis replicas 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 replica 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.{{cite web |url=https://code.google.com/p/redis/wiki/ReplicationHowto |title=Google Code Archive - Long-term storage for Google Code Project Hosting. |website=code.google.com}}

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 or double-threaded when it rewrites the AOF (append-only file).{{cite web |url=http://antirez.com/news/111 |title=Redis on the Raspberry Pi: adventures in unaligned lands - antirez |website=antirez.com}} Thus, a single Redis instance cannot use parallel execution of tasks such as stored procedures.

Redis introduced clustering in April 2015 with the release of version 3.0.{{cite web |url=https://github.com/antirez/redis/blob/3.0/00-RELEASENOTES |title=Redis 3.0 Release Notes |website=GitHub |access-date=2017-03-10}} The cluster specification implements a subset of Redis commands: all single-key commands are available, multi-key operations (commands related to unions and intersections) are restricted to keys belonging to the same node, and commands related to database selection operations are unavailable.{{cite web |url=https://redis.io/topics/cluster-spec#implemented-subset |title=Cluster Spec |access-date=2017-03-10}} A Redis cluster can scale up to 1,000 nodes, achieve "acceptable" write safety and to continue operations when some nodes fail.{{cite web |url=https://redis.io/topics/cluster-spec |title=Cluster Spec |access-date=2017-03-10}}{{cite web |url=https://redis.io/topics/cluster-tutorial |title=Cluster Tutorial |access-date=2017-03-10}}

Due to the nature of the database design, typical use cases are session caching, full page cache, message queue applications, leaderboards and counting among others.{{cite web |url=http://objectrocket.com/blog/how-to/top-5-redis-use-cases |title=Top 5 Redis use cases - ObjectRocket |date=7 November 2017 |website=ObjectRocket |publisher=Rackspace}} The publish–subscribe messaging paradigm allows real-time communication between servers.

Amazon Web Services offers a managed Redis service called ElastiCache for Redis, Google offers a managed Redis service called Cloud Memorystore,{{Cite web |title=Memorystore: in-memory data store |url=https://cloud.google.com/memorystore |access-date=2023-02-03 |website=Google Cloud |language=en}} Microsoft offers Azure Cache for Redis in Azure,{{cite web |url=https://azure.microsoft.com/en-us/services/cache/ |title=Azure Redis Cache - Redis cache cloud service - Microsoft Azure |website=azure.microsoft.com}} and Alibaba offers ApsaraDB for Redis in Alibaba Cloud.{{cite web |url=https://www.alibabacloud.com/product/apsaradb-for-redis |title=ApsaraDB for Redis: A Key Value Database Service - Alibaba Cloud|website=www.alibabacloud.com}}

Redis has been used by companies including Twitter,{{Cite web |title=Scaling Redis at Twitter |date=31 August 2014 |url=https://www.youtube.com/watch?v=rP9EKvWt0zo |access-date=2023-07-22 |language=en}}{{Cite web |title=Using Redis at Scale at Twitter - by Rashmi Ramesh of Twitter - RedisConf17 - |date=5 July 2017 |url=https://www.youtube.com/watch?v=QznaOSk20nU |access-date=2023-07-22 |language=en}} Airbnb,{{Cite web |title=AWS re:Invent 2018: Airbnb's Journey from Self-Managed Redis to ElastiCache for Redis (DAT319) |date=28 November 2018 |url=https://www.youtube.com/watch?v=eyd_8efUCwM |access-date=2023-07-22 |language=en}} Tinder,{{Cite web |date=2020-01-30 |title=Building resiliency at scale at Tinder with Amazon ElastiCache {{!}} AWS Database Blog |url=https://aws.amazon.com/blogs/database/building-resiliency-at-scale-at-tinder-with-amazon-elasticache/ |access-date=2023-07-22 |website=aws.amazon.com |language=en-US}} Yahoo,{{Cite web |title=AWS re:Invent 2022 - How Yahoo cost optimizes their in-memory workloads with AWS (DAT321) |date=2 December 2022 |url=https://www.youtube.com/watch?v=jEwrcpq2mLM |access-date=2023-07-22 |language=en}} Adobe,{{Cite web|title=AWS re:Invent 2014 {{!}} (SDD402) Amazon ElastiCache Deep Dive |date=17 November 2014 |url=https://www.youtube.com/watch?v=cEkHBqhQnog |access-date=2023-07-22 |language=en}} Hulu,{{Cite web |title=Hulu Case Study |url=https://aws.amazon.com/solutions/case-studies/hulu/ |access-date=2023-07-22 |website=Amazon Web Services, Inc. |language=en-US}} Amazon{{Cite web |title=Amazon GameOn Database Migration Case Study – Amazon Web Services (AWS) |url=https://aws.amazon.com/solutions/case-studies/amazon-gameon/ |access-date=2023-07-22 |website=Amazon Web Services, Inc. |language=en-US}} and OpenAI.{{Cite web |title=Elevated API Errors |url=https://status.openai.com/incidents/fk0tcbydtybr |access-date=2023-10-28 |website=status.openai.com |language=en}}

• Conflict-free replicated data type
• Memcached
• Infinispan
• Valkey

{{Reflist}}

{{Refbegin}}

• Isabel Drost and Jan Lehnard (29 October 2009), [http://www.h-online.com/open/features/Happenings-NoSQL-Conference-Berlin-843597.html Happenings: NoSQL Conference, Berlin], The H. [http://nosqlberlin.de/slides/NoSQLBerlin-Redis.pdf Slides] for the Redis presentation. [http://www.paperplanes.de/2009/10/27/theres_something_about_redis.html Summary].
• Billy Newport (IBM): "[http://www.infoq.com/presentations/newport-evolving-key-value-programming-model Evolving the Key/Value Programming Model to a Higher Level]" Qcon Conference 2009 San Francisco.
• A Mishra: "[http://blog.andolasoft.com/2013/07/how-to-install-and-configure-redis-server-on-centosfedora-server.html Install and configure Redis on Centos/ Fedora server]".
• E. Mouzakitis: "[https://www.datadoghq.com/blog/how-to-monitor-redis-performance-metrics/ Monitoring Redis Performance]"{{Refend}}

• {{Official website|https://redis.io}}
• [https://github.com/valkey-io/valkey Valkey: Ongoing development home of the original BSD-licensed Redis software]

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{{DEFAULTSORT:Redis}}

Category:C (programming language) software

Category:Database caching

Category:Database management systems

Category:Distributed computing architecture

Category:Key-value databases

Category:Lua (programming language)-scriptable software

Category:NoSQL

Category:Software using the Server Side Public License

Category:Structured storage

Category:In-memory database management systems