|Initial release||August 17, 2009|
2.9.0 / May 17, 2019
|Operating system||Linux, BSD, macOS, Solaris|
|Type||NoSQL database, cloud storage|
|License||Apache License 2.0|
Riak (pronounced "ree-ack" ) is a distributed NoSQL key-value data store that offers high availability, fault tolerance, operational simplicity, and scalability. In addition to the open-source version, it comes in a supported enterprise version and a cloud storage version. Riak implements the principles from Amazon's Dynamo paper with heavy influence from the CAP Theorem. Written in Erlang, Riak has fault tolerant data replication and automatic data distribution across the cluster for performance and resilience.
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- Fault-tolerant availability
- Riak replicates key/value stores across a cluster of nodes with a default n_val of three. In the case of node outages due to network partition or hardware failures, data can still be written to a neighboring node beyond the initial three, and read-back due to its "masterless" peer-to-peer architecture.
- Predictable latency
- Riak distributes data across nodes with hashing and can provide latency profile, even in the case of multiple node failures.
- Storage options
- Keys/values can be stored in memory, disk, or both.
- Multi-datacenter replication
- In multi-datacenter replication, one cluster acts as a "primary cluster." The primary cluster handles replication requests from one or more "secondary clusters" (generally located in other regions or countries). If the datacenter with the primary cluster goes down, a second cluster can take over as the primary cluster.
- There are two primary modes of operation: fullsync and realtime. In fullsync mode, a complete synchronization occurs between primary and secondary cluster(s), by default every six hours. In real-time mode,replication to the secondary data center(s) is triggered by updates to the primary data center. All multi-datacenter replication occurs over multiple concurrent TCP connections to maximize performance and network utilization.
- Tunable consistency
- Option to choose between eventual and strong consistency for each bucket.
Licensing and support
Riak is available for free under the Apache 2 License. In addition, Basho Technologies offered two options for its commercial software, Riak Enterprise and Riak Enterprise Plus. Riak Enterprise Plus adds baseline and annual system health checks to ensure long-term platform stability and performance.
Riak was originally written by Andy Gross and others at Basho Technologies  to power a web Sales Force Automation application by former engineers and executives from Akamai. There was more interest in the datastore technology than the applications built on it, so the company decided to build a business around Riak itself, gaining adoption throughout the Fortune 100 and becoming a foundation to many of the world's fastest-growing Web-based, mobile and social networking applications, as well as cloud service providers. Releases after graduation include
- 1.1, released Feb 21 2012, added Riaknostic, enhanced error logging and reporting, improved resiliency for large clusters, and a new graphical operations and monitoring interface called Riak Control.
- 1.4, released July 10, 2013, added counters, secondary indexing improvements, reduced object storage overhead, handoff progress reporting, and enhancements to MDC replication.
- 2.0, released September 2, 2014, added new data types including sets, maps, registers, and flags simplifying application development. Strong consistency by bucket, full-text integration with Apache Solr, Security, and reduced replicas for Secondary sites.
- 2.1, released April 16, 2015, added an optimization for many write-heavy workloads – “write once” buckets – buckets whose entries are intended to be written exactly once, and never updated or over-written.
- 2.2, released November 17, 2016, added Support for Debian 8 and Ubuntu 16.04, Solr integration improvements.
- Riak may no longer be maintained by Basho 
- 2.2.5, released April 26, 2018, is the first community release. Added support for Multi-Datacentre Replication which was not part of open-source Riak before, added a grow-only set data type, improved data distribution over nodes and cleaned up production test issues.
- 2.9.0, released May 15, 2019 is the latest release.
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