Redis

From Wikipedia, the free encyclopedia

This is an old revision of this page, as edited by Mike Dillon (talk | contribs) at 18:54, 17 June 2014 (link to Pivotal Software). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

This article is about Redis software. For Redis people, see Romani people.
Redis
Developer(s)Salvatore Sanfilippo
Initial releaseApril 10, 2009 (2009-04-10)
Stable release
2.8.10 / June 5, 2014 (2014-06-05)
Repository
Written inANSI C
Operating systemCross-platform
Available inEnglish
TypeKey–value stores
LicenseBSD
Websiteredis.io

Redis is an open-source, networked, in-memory, key-value data store with optional durability. It is written in ANSI C. The development of Redis has been sponsored by Pivotal Software since May 2013;[1] before that, it was sponsored by VMware.[2][3] According to the monthly ranking by DB-Engines.com, Redis is the most popular key-value store.[4] The name Redis means REmote DIctionary Server.[5]

Supported languages

Many languages have Redis bindings, including:[6] ActionScript, C, C++, C#, Clojure, Common Lisp, Dart, Erlang, Go, Haskell, Haxe, Io, Java, JavaScript (Node.js), Lua, Objective-C, Perl, PHP, Pure Data, Python, R,[7] Ruby, Scala, Smalltalk and Tcl.

Data models

In its outer layer, the Redis data model is a dictionary which maps keys to values. One of the main differences 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)
  • Hashes where keys and values are strings

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.

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 [8] in which some of the dataset is stored on disk, but this feature is deprecated. Persistence is now reached 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 syncs data to the disk 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.[9]

Replication

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 are writable, 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.[10]

Performance

When the durability of data is not needed, the in-memory nature of Redis allows it to perform extremely well compared to database systems that write every change to disk before considering a transaction committed.[11] There is no notable speed difference between write and read operations. Redis operates as a single process and single-threaded. Therefore a single Redis instance cannot utilize parallel execution of tasks e.g. stored procedures (Lua scripts).

Clustering

The Redis project has a cluster specification,[12] but the cluster feature is currently in Beta stage.[13] According to a news post by Redis creator Sanfilippo, the first production version of Redis cluster (planned for beta release at end of 2013),[14] will support automatic partitioning of the key space and hot resharding, but will support only single key operations.[15] In 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.[12][13][16]

Cloud deployment

Redis is commonly deployed on IaaS or PaaS platforms like Amazon Web Services, Rackspace or Heroku.

On IaaS platforms, it is possible to deploy Redis by uploading a virtual machine image, with Redis installed, to a cloud machine instance. Alternatively, it is possible to install Redis on an already-running machine instance.

On both IaaS and PaaS platforms, there are commercial database as a service providers which allow applications to use Redis as a managed service, without physically launching a virtual machine instance for the database. These services handle installation, configuration and maintenance of Redis on behalf of the application owner. Following are notable examples of commercial Redis database as a service providers.

Provider Available On Managed Service Features Pricing Model
Amazon Web Services - ElastiCache[20]

Amazon EC2

  • Automatic healing of failed nodes
  • Resilient system to prevent overloaded DBs
  • Performance monitoring
  • Free for 750 hours on micro instance[21]
  • Pay per use for machine utilization, no separate charge for data usage[22]
RedisToGo[23] Amazon EC2, Rackspace, Heroku, AppHarbor, Orchestra
  • Daily backups
  • API enabling creation, deletion, or download of Redis instances
  • Automatic export/import of database to new instance on upgrade
  • Free up to 5MB (memory)[23]
  • Paid plans based on memory usage and number of databases
Redis Cloud (Redis Labs)[24] Amazon EC2, Windows Azure, IBM SoftLayer, Google Cloud Platform, Heroku, Cloud Foundry, OpenShift, AppFog, AppHarbor
  • Automatic scaling, unlimited Redis nodes
  • High availability
  • Data persistence and durability
  • Daily and on-demand backups
  • Built-in clustering
  • Free up to 25MB (memory)[25]
  • Pay per use, or paid plans based on memory usage and functionality - high availability and Multi-AZ.

See also

References

  1. ^ Redis Sponsors – Redis
  2. ^ VMware: the new Redis home
  3. ^ VMWare: The Console: VMware hires key developer for Redis
  4. ^ DB-Engines Ranking of Key-value Stores
  5. ^ http://redis.io/topics/faq
  6. ^ Redis language bindings
  7. ^ CRAN – Package rredis
  8. ^ Redis documentation "Virtual Memory", redis.io, accessed January 18, 2011.
  9. ^ Redis persistence demystified
  10. ^ ReplicationHowto – redis – A persistent key-value database with built-in net interface written in ANSI-C for Posix systems – Google Project Hosting
  11. ^ "FAQ".
  12. ^ a b Redis Cluster Specification, Redis.io, Retrieved 2013-12-25.
  13. ^ a b Redis Cluster Tutorial, Redis.io, Retrieved 2014-06-14.
  14. ^ Redis Download Page, Redis.io, Retrieved 2013-12-25.
  15. ^ News about Redis: 2.8 is shaping, I'm back on Cluster, Antirez Weblog - Salvatore Sanfilippo, Retrieved 2013-12-25.
  16. ^ Redis Cluster - a Pragmatic Approach to Distribution, Redis.io, Retrieved 2013-12-25.
  17. ^ "Install Redis.sh", GitHub Gist, Retrieved 2013-12-29.
  18. ^ "Running Redis on a CentOS Linux VM in Windows Azure", Thomas Conté's MSDN Weblog, Retrieved 2013-12-29.
  19. ^ "Install Redis On Joyent" Daniel Jackoway, Retrieved 2014-01-14.
  20. ^ "Amazon ElastiCache", Amazon Web Services, Retrieved 2013-12-29.
  21. ^ "Amazon ElastiCache Free Usage Tier", Amazon Web Services, Retrieved 2013-12-29.
  22. ^ "Amazon ElastiCache Pricing", Amazon Web Services, Retrieved 2013-12-29.
  23. ^ a b "RedisToGo Documentation", RedisToGo.com, Retrieved 2013-12-29.
  24. ^ Redis Cloud by Redis Labs, Redis-Cloud.com, Retrieved 2013-12-29.
  25. ^ "Redis Labs Pricing", RedisLabs.com, Retrieved 2013-12-29.

External links

Retrieved from "https://en.wikipedia.org/w/index.php?title=Redis&oldid=613319944"