Elliptics is a distributed key–value data storage with

open source Open source is source code that is made freely available for possible modification and redistribution. Products include permission to use and view the source code, design documents, or content of the product. The open source model is a decentrali ...

code. By default it is a classic

distributed hash table A distributed hash table (DHT) is a Distributed computing, distributed system that provides a lookup service similar to a hash table. Key–value pairs are stored in a DHT, and any participating node (networking), node can efficiently retrieve the ...

(DHT) with multiple replicas put in different groups (distributed hashes). Elliptics was created to meet requirements of multi-datacenter and physically distributed storage locations when storing huge amount of medium and large files (1 KB up to gigabytes in size, thousands to billions of objects).

History

Elliptics was created in 2007, initially as a part of POHMELFS, a cache coherent

distributed file system A clustered file system (CFS) is a file system which is shared by being simultaneously Mount (computing), mounted on multiple Server (computing), servers. There are several approaches to computer cluster, clustering, most of which do not emplo ...

developed by Linux programmer Evgeniy Polyakov. POHMELFS was announced on January 31, 2008, and merged into the staging area of the

Linux kernel The Linux kernel is a Free and open-source software, free and open source Unix-like kernel (operating system), kernel that is used in many computer systems worldwide. The kernel was created by Linus Torvalds in 1991 and was soon adopted as the k ...

source tree in version 2.6.30, released June 9, 2009. The filesystem went practically unused and was removed again in February 2012. In 2008 Elliptics separated as an independent project. Polyakov tried different approaches to distributed data storage systems, some of them were not suitable because of their complexity and some of them were too far from a real-life ( BerkeleyDB,

LevelDB LevelDB is an open-source on-disk key-value store written by Google fellows Jeffrey Dean and Sanjay Ghemawat. Inspired by Bigtable, LevelDB source code is hosted on GitHub under the New BSD License and has been ported to a variety of Unix-base ...

, Kyoto Cabinet backends for medium and big files, different datacenters in a single DHT ring, non eventual recovery). Elliptics is eventually consistent system with multiple updated in parallel

replicas A replica is an exact (usually 1:1 in scale) copy or remake of an object, made out of the same raw materials, whether a molecule, a work of art, or a commercial product. The term is also used for copies that closely resemble the original, without ...

potentially living in physically distributed locations. Elliptics contains multiple layers from low-level on-disk store (named Eblob) up to SLRU caches and dynamic routing protocol. In 2012, Polyakov announced a new version of POHMELFS based on Elliptics. As of 2014, Elliptics is used in

Yandex Yandex LLC ( rus, Яндекс, r=Yandeks, p=ˈjandəks) is a Russian technology company that provides Internet-related products and services including a web browser, search engine, cloud computing, web mapping, online food ordering, streaming ...

Maps A map is a symbolic depiction of interrelationships, commonly spatial, between things within a space. A map may be annotated with text and graphics. Like any graphic, a map may be fixed to paper or other durable media, or may be displayed on ...

, Disk, Music, Photos, Market and infrastructure, Sputnik search engine and Coub.

Architecture

By default, Elliptics forms a distributed hash table in single group (a replica). Group may contains one or many servers as well as physical server can contain multiple elliptics groups (replicas) stored on different backends. Groups can live in different physical locations thus allowing to serve clients' requests when other locations are not accessible. A

peer-to-peer Peer-to-peer (P2P) computing or networking is a distributed application architecture that partitions tasks or workloads between peers. Peers are equally privileged, equipotent participants in the network, forming a peer-to-peer network of Node ...

(P2P) protocol can be used to access data directly from storage servers without proxying. Elliptics supports server-side scripting in C++,

JavaScript JavaScript (), often abbreviated as JS, is a programming language and core technology of the World Wide Web, alongside HTML and CSS. Ninety-nine percent of websites use JavaScript on the client side for webpage behavior. Web browsers have ...

Python Python may refer to: Snakes * Pythonidae, a family of nonvenomous snakes found in Africa, Asia, and Australia ** ''Python'' (genus), a genus of Pythonidae found in Africa and Asia * Python (mythology), a mythical serpent Computing * Python (prog ...

, based on the

Cocaine Cocaine is a tropane alkaloid and central nervous system stimulant, derived primarily from the leaves of two South American coca plants, ''Erythroxylum coca'' and ''Erythroxylum novogranatense, E. novogranatense'', which are cultivated a ...

technology, SLRU cache and multiple pluggable backends (eblob is the fastest for medium and large data and the most popular one). Elliptics clients connect directly to all storage servers which helps to: * Execute

lookup In computer science, a lookup table (LUT) is an array that replaces runtime computation of a mathematical function with a simpler array indexing operation, in a process termed as ''direct addressing''. The savings in processing time can be sig ...

in ''O''(1) network requests (single network request per replica) * Run write/update commands into multiple replicas in parallel There are several

application programming interface An application programming interface (API) is a connection between computers or between computer programs. It is a type of software Interface (computing), interface, offering a service to other pieces of software. A document or standard that des ...

s (APIs) for data access: * Asynchronous feature-promise C++ library * Python binding * Go binding * HTTP-proxy named Rift with buckets and ACLs based on TheVoid library (using boost::asio) * Community-driven Erlang bindings

Features

* Distributed hash tables, no metadata servers, true horizontal scaling * Data replication – replicas can be stored in different physical locations * Range and bulk requests * Different I/O storage backends, API to create own low-level storage backends * Automatic data repartitioning in case of removed or added nodes * Eventually consistent recovery * Consistent hashing addressing model * Cluster statistics * Frontend: HTTP; bindings: C/ C++, Go,

* Server-side script execution support (write trigger analog) * Distributed SLRU cache with TTL * P2P streaming support (eblob and file backends only - external applications like

Nginx (pronounced "engine x" , stylized as NGINX or nginx) is a web server that can also be used as a reverse proxy, load balancer, mail proxy and HTTP cache. The software was created by Russian developer Igor Sysoev and publicly released in 20 ...

web server can stream data from eblob object files directly to clients without proxying)

Problems and restrictions

Eventual consistency Eventual consistency is a consistency model used in distributed computing to achieve high availability. Put simply: if no new updates are made to a given data item, ''eventually'' all accesses to that item will return the last updated value. Eve ...

: as Elliptics is fully distributed in case of emergency server can possibly return a file copy which is older than an actual one. Sometimes it can be unacceptable. In these cases due to time loses it is better to use more reliable ways of data request. * Network between client and servers can become a weak point as data is written on several servers in parallel. * API may be inconvenient for high-level requests. Elliptics does not provide its users with SQL-like data requests. * Elliptics does not have high-level transactions support that is why it is impossible to guarantee that a command group will be fully executed or will not be executed at all. * Transactions are only atomic within group and are locked based on primary key.

Documentation

Elliptics and its supporting projects are being documented at communit
wiki
. It contains high-level design docs, tutorial, low-level details and knowledge base. Elliptics and related projects are discussed in open Googl
group

References

External links

* . {{Cloud computing Key-value databases Software using the GNU Lesser General Public License NoSQL products Yandex software