Redis (;
Remote Dictionary Server)
is an in-memory data structure store, used as a
distributed,
in-memory key–value database
In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases ...
, cache and
message broker, with optional
durability
Durability is the ability of a physical product to remain functional, without requiring excessive maintenance or repair, when faced with the challenges of normal operation over its design lifetime. There are several measures of durability in us ...
. Redis supports different kinds of
abstract data structures
In computer science, an abstract data type (ADT) is a mathematical model for data types. An abstract data type is defined by its behavior ( semantics) from the point of view of a '' user'', of the data, specifically in terms of possible values ...
, such as
strings,
lists
A ''list'' is any set of items in a row. List or lists may also refer to:
People
* List (surname)
Organizations
* List College, an undergraduate division of the Jewish Theological Seminary of America
* SC Germania List, German rugby union ...
,
maps,
sets, sorted sets,
HyperLogLog
HyperLogLog is an algorithm for the count-distinct problem, approximating the number of distinct elements in a multiset. Calculating the ''exact'' cardinality of the distinct elements of a multiset requires an amount of memory proportional to the ...
s,
bitmaps,
streams
A stream is a continuous body of surface water flowing within the bed and banks of a channel. Depending on its location or certain characteristics, a stream may be referred to by a variety of local or regional names. Long large streams a ...
, and
spatial indices. The project was developed and maintained by Salvatore Sanfilippo, starting in 2009. From 2015 until 2020, he led a project core team sponsored by
Redis Labs
Redis Ltd. (originally Redis Labs, Garantia Data) is a private computer software company headquartered in Mountain View, California. Redis is the sponsor of the open-source in-memory NoSQL database of the same name and the provider of Redis Enter ...
.
Salvatore Sanfilippo left Redis as the maintainer in 2020. It is
open-source software
Open-source software (OSS) is computer software that is released under a license in which the copyright holder grants users the rights to use, study, change, and distribute the software and its source code to anyone and for any purpose. ...
released under a
BSD 3-clause license.
In 2021, not long after the original author and main maintainer left, Redis Labs dropped the Labs from its name and now is known simply as "Redis".
History
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
Real-time or real time describes various operations in computing or other processes that must guarantee response times within a specified time (deadline), usually a relatively short time. A real-time process is generally one that happens in defined ...
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. 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
Hacker News (sometimes abbreviated as HN) is a social news website focusing on computer science and entrepreneurship. It is run by the investment fund and startup incubator Y Combinator. In general, content that can be submitted is defined as " ...
. The project began to get traction, particularly among the Ruby community, with
GitHub
GitHub, Inc. () is an Internet hosting service for software development and version control using Git. It provides the distributed version control of Git plus access control, bug tracking, software feature requests, task management, cont ...
and
Instagram
Instagram is a photo and video sharing social networking service owned by American company Meta Platforms. The app allows users to upload media that can be edited with filters and organized by hashtags and geographical tagging. Posts can ...
being among the first companies adopting it.
Sanfilippo was hired by
VMware
VMware, Inc. is an American cloud computing and virtualization technology company with headquarters in Palo Alto, California. VMware was the first commercially successful company to virtualize the x86 architecture.
VMware's desktop software ru ...
in March, 2010.
In May, 2013, Redis was sponsored by
Pivotal Software
Pivotal Software, Inc. was an American multinational software and services company based in San Francisco that provided cloud platform hosting and consulting services. Since December 2019, Pivotal has been part of VMware.
History
Pivotal ...
(a VMware spin-off).
In June 2015, development became sponsored by
Redis Labs
Redis Ltd. (originally Redis Labs, Garantia Data) is a private computer software company headquartered in Mountain View, California. Redis is the sponsor of the open-source in-memory NoSQL database of the same name and the provider of Redis Enter ...
.
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.
In June 2020, Salvatore Sanfilippo stepped down as Redis maintainer.
Differences from other database systems
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
A relational database is a (most commonly digital) database based on the relational model of data, as proposed by E. F. Codd in 1970. A system used to maintain relational databases is a relational database management system (RDBMS). Many relati ...
(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 creates an in-memory copy of the data on disk.
Popularity
According to monthly
DB-Engines rankings, Redis is often the most popular
key–value database. Redis has also been ranked the #4
NoSQL
A NoSQL (originally referring to "non- SQL" or "non-relational") database provides a mechanism for storage and retrieval of data that is modeled in means other than the tabular relations used in relational databases. Such databases have existed ...
database in user satisfaction and market presence based on user reviews, the most popular NoSQL database in containers, and the #4 Data store of 2019 by ranking website stackshare.io. It was voted most loved database in the
Stack Overflowbr>
Developer Surveyin 2017, 2018, 2019, 2020 and 2021.
Supported languages
Since version 2.6, Redis features
server-side
In the client–server model, server-side refers to programs and operations that run on the server. This is in contrast to client-side programs and operations which run on the client.
General concepts
Typically, a server is a computer applicati ...
scripting in the language
Lua.
Many
programming language
A programming language is a system of notation for writing computer programs. Most programming languages are text-based formal languages, but they may also be graphical. They are a kind of computer language.
The description of a programming ...
s have Redis
language bindings on the client side, including:
ActionScript
ActionScript is an object-oriented programming language originally developed by Macromedia Inc. (later acquired by Adobe). It is influenced by HyperTalk, the scripting language for HyperCard. It is now an implementation of ECMAScript (meaning ...
,
C,
C++,
C#,
Chicken
The chicken (''Gallus gallus domesticus'') is a domesticated junglefowl species, with attributes of wild species such as the grey and the Ceylon junglefowl that are originally from Southeastern Asia. Rooster or cock is a term for an adu ...
,
Clojure,
Common Lisp
Common Lisp (CL) is a dialect of the Lisp programming language, published in ANSI standard document ''ANSI INCITS 226-1994 (S20018)'' (formerly ''X3.226-1994 (R1999)''). The Common Lisp HyperSpec, a hyperlinked HTML version, has been derived fr ...
,
Crystal
A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macro ...
,
D,
Dart
Dart or DART may refer to:
* Dart, the equipment in the game of darts
Arts, entertainment and media
* Dart (comics), an Image Comics superhero
* Dart, a character from ''G.I. Joe''
* Dart, a ''Thomas & Friends'' railway engine character
* Da ...
,
Delphi
Delphi (; ), in legend previously called Pytho (Πυθώ), in ancient times was a sacred precinct that served as the seat of Pythia, the major oracle who was consulted about important decisions throughout the ancient classical world. The orac ...
,
Elixir,
Erlang,
Go,
Haskell,
Haxe
Haxe is an open source high-level cross-platform programming language and compiler that can produce applications and source code, for many different computing platforms from one code-base. It is free and open-source software, released under the ...
,
Io,
Java
Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mo ...
,
Nim,
JavaScript
JavaScript (), often abbreviated as JS, is a programming language that is one of the core technologies of the World Wide Web, alongside HTML and CSS. As of 2022, 98% of websites use JavaScript on the client side for webpage behavior, of ...
(
Node.js
Node.js is an open-source server environment. Node.js is cross-platform and runs on Windows, Linux, Unix, and macOS. Node.js is a back-end JavaScript runtime environment. Node.js runs on the V8 JavaScript Engine and executes JavaScript cod ...
),
Julia,
Lua,
Objective-C,
OCaml,
Perl
Perl is a family of two high-level, general-purpose, interpreted, dynamic programming languages. "Perl" refers to Perl 5, but from 2000 to 2019 it also referred to its redesigned "sister language", Perl 6, before the latter's name was offic ...
,
PHP,
Pure Data,
Python,
R,
Racket,
Ruby
A ruby is a pinkish red to blood-red colored gemstone, a variety of the mineral corundum ( aluminium oxide). Ruby is one of the most popular traditional jewelry gems and is very durable. Other varieties of gem-quality corundum are called ...
,
Rust
Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO( ...
,
Scala,
Smalltalk
Smalltalk is an object-oriented, dynamically typed reflective programming language. It was designed and created in part for educational use, specifically for constructionist learning, at the Learning Research Group (LRG) of Xerox PARC by Alan ...
,
Swift, and
Tcl. Several client software programs exist in these languages.
Data types
Redis maps keys to types of values. An important difference between Redis and other
structured storage
Structuring, also known as smurfing in banking jargon, is the practice of executing financial transactions such as making bank deposits in a specific pattern, calculated to avoid triggering financial institutions to file reports required by la ...
systems is that Redis supports not only
strings, but also abstract data types:
*
Lists
A ''list'' is any set of items in a row. List or lists may also refer to:
People
* List (surname)
Organizations
* List College, an undergraduate division of the Jewish Theological Seminary of America
* SC Germania List, German rugby union ...
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
*
HyperLogLog
HyperLogLog is an algorithm for the count-distinct problem, approximating the number of distinct elements in a multiset. Calculating the ''exact'' cardinality of the distinct elements of a multiset requires an amount of memory proportional to the ...
s used for approximated set cardinality size estimation, available since Redis 2.8.9 in April 2014.
*
Stream
A stream is a continuous body of surface water flowing within the bed and banks of a channel. Depending on its location or certain characteristics, a stream may be referred to by a variety of local or regional names. Long large streams ...
of entries with consumer groups, allows you to store multiple fields and string values with an automatic, time-based sequence at a single key, available since Redis 5.0 in October 2018
* Geospatial data through the implementation of the
geohash technique, available since Redis 3.2.
The type of a value determines what operations (called commands) are available for the value. Redis supports high-level, atomic, server-side operations like intersection, union, and difference between sets and sorting of lists, sets and sorted sets.
More data types are supported based on Redis Modules API:
*
JSON – RedisJSON implements ECMA-404 (the JavaScript Object Notation Data Interchange Standard) as a native data type.
*
Graph – RedisGraph implements a queryable property graph
*
Time series
In mathematics, a time series is a series of data points indexed (or listed or graphed) in time order. Most commonly, a time series is a sequence taken at successive equally spaced points in time. Thus it is a sequence of discrete-time data. Ex ...
– RedisTimeSeries implements a time series data structure
*
Bloom filter
A Bloom filter is a space-efficient probabilistic data structure, conceived by Burton Howard Bloom in 1970, that is used to test whether an element is a member of a set. False positive matches are possible, but false negatives are not – in ...
,
Cuckoo filter,
Count–min sketch
In computing, the count–min sketch (CM sketch) is a probabilistic data structure that serves as a frequency table of events in a stream of data. It uses hash functions to map events to frequencies, but unlike a hash table uses only sub-linear ...
, and Top-K – RedisBloom implements a set of probabilistic data structures for Redis
Persistence
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 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.
Replication
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.
Performance
When the
durability
Durability is the ability of a physical product to remain functional, without requiring excessive maintenance or repair, when faced with the challenges of normal operation over its design lifetime. There are several measures of durability in us ...
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).
Thus, a single Redis instance cannot use parallel execution of tasks such as
stored procedure
A stored procedure (also termed proc, storp, sproc, StoPro, StoredProc, StoreProc, sp, or SP) is a subroutine available to applications that access a relational database management system (RDBMS). Such procedures are stored in the database data d ...
s.
Clustering
Redis introduced clustering in April 2015 with the release of version 3.0.
The
cluster
may refer to:
Science and technology Astronomy
* Cluster (spacecraft), constellation of four European Space Agency spacecraft
* Asteroid cluster, a small asteroid family
* Cluster II (spacecraft), a European Space Agency mission to study th ...
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.
A Redis cluster can scale up to 1,000 nodes, achieve "acceptable" write safety and to continue operations when some nodes fail.
Use cases
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.
The publish–subscribe messaging paradigm allows real-time communication between servers.
Large companies such as Twitter are using Redis,
Amazon Web Services offers a managed Redis service called
ElastiCache for Redis,
Microsoft
Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washi ...
offers Azure Cache for Redis in
Azure,
and
Alibaba offers ApsaraDB for Redis in
Alibaba Cloud.
See also
*
Conflict-free replicated data type
*
Memcached
Memcached (pronounced variously ''mem-cash-dee'' or ''mem-cashed'') is a general-purpose distributed memory-caching system. It is often used to speed up dynamic database-driven websites by caching data and objects in RAM to reduce the number of ...
*
Infinispan
Infinispan is a distributed cache and key-value NoSQL data store software developed by Red Hat. Java applications can embed it as library, use it as a service in WildFly or any non-java applications can use it as remote service through TCP/IP ...
References
Further reading
* Isabel Drost and Jan Lehnard (29 October 2009)
Happenings: NoSQL Conference, Berlin The H
Heise (officially ''Heise Gruppe'', formerly ''Verlag Heinz Heise'') is a German media conglomerate headquartered in Hanover, Lower Saxony. It was founded in 1949 by and is still family-owned. Its core business is directory media as well as ...
Slidesfor the Redis presentation
* Billy Newport (IBM):
Evolving the Key/Value Programming Model to a Higher Level Qcon Conference 2009 San Francisco.
* A Mishra:
.
* E. Mouzakitis:
Monitoring Redis Performance
External links
*
{{DEFAULTSORT:Redis
Distributed computing architecture
Free database management systems
Free software programmed in C
Key-value databases
Lua (programming language)-scriptable software
NoSQL
Software using the BSD license
Structured storage