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### What is Citus?

* **Open-source** PostgreSQL extension (not a fork)
* **Scalable** across multiple hosts through sharding and replication
* **Distributed** engine for query parallelization
* **Highly available** in the face of host failures

Citus horizontally scales PostgreSQL across commodity servers using
sharding and replication. Its query engine parallelizes incoming
SQL queries across these servers to enable real-time responses on
large datasets.

Citus extends the underlying database rather than forking it, which
gives developers and enterprises the power and familiarity of a
traditional relational database. As an extension, Citus supports
new PostgreSQL releases, allowing users to benefit from new features
while maintaining compatibility with existing PostgreSQL tools.
Note that Citus supports many (but not all) SQL commands; see the
[FAQ][faq] for more details.

Common Use-Cases:
* Powering real-time analytic dashboards
* Exploratory queries on events as they happen
* Large dataset archival and reporting
* Session analytics (funnels, segmentation, and cohorts)

To learn more, visit [citusdata.com](https://www.citusdata.com) and join
the [mailing list](https://groups.google.com/forum/#!forum/citus-users) to
stay on top of the latest developments.

### Quickstart

#### Local Citus Cluster

* Install docker-compose: [Mac][mac_install] | [Linux][linux_install]
* (Mac only) connect to Docker VM
  ```bash
  eval $(docker-machine env default)
  ```

* Pull and start the docker images
  ```bash
  wget https://raw.githubusercontent.com/citusdata/docker/master/docker-compose.yml
  docker-compose -p citus up -d
  ```

* Connect to the master database
  ```bash
  docker exec -it citus_master psql -U postgres -d postgres
  ```

* Follow the [first tutorial][tutorial] instructions
* To shut the cluster down, run

  ```bash
  docker-compose -p citus down
  ```

### Talk to Contributors and Learn More

<table class="tg">
<col width="45%">
<col width="65%">
<tr>
  <td>Documentation</td>
  <td>Try the <a
  href="http://docs.citusdata.com/en/v5.1/tutorials/tut-cluster.html">Citus
  tutorials</a> for a hands-on introduction or <br/>the <a
  href="http://docs.citusdata.com/en/v5.1/index.html">documentation</a> for
  a more comprehensive reference.</td>
</tr>
<tr>
  <td>Google Groups</td>
  <td>The <a
  href="https://groups.google.com/forum/#!forum/citus-users">Citus Google
  Group</a> is our place for detailed questions and discussions.</td>
</tr>
<tr>
  <td>Slack</td>
  <td>Chat with us in our community <a
  href="https://slack.citusdata.com">Slack channel</a>.</td>
</tr>
<tr>
  <td>Github Issues</td>
  <td>We track specific bug reports and feature requests on our <a
  href="https://github.com/citusdata/citus/issues">project
  issues</a>.</td>
</tr>
<tr>
  <td>Twitter</td>
  <td>Follow <a href="https://twitter.com/citusdata">@citusdata</a>
  for general updates and PostgreSQL scaling tips.</td>
</tr>
<tr>
  <td>Training and Support</td>
  <td>See our <a
  href="https://www.citusdata.com/citus-products/citus-data-pricing">support
  page</a> for training and dedicated support options.</td>
</tr>
</table>

### Contributing

Citus is built on and of open source. We welcome your contributions,
and have added a
[helpwanted](https://github.com/citusdata/citus/labels/helpwanted) label
to issues which are accessible to new contributors. The
[CONTRIBUTING.md](CONTRIBUTING.md) file explains how to get started
developing the Citus extension itself and our code quality guidelines.

### Who is Using Citus?

Citus is deployed in production by many customers, ranging from
technology start-ups to large enterprises. Here are some examples:

* [CloudFlare](https://www.cloudflare.com/) uses Citus to provide
real-time analytics on 100 TBs of data from over 4 million customer
websites. [Case
Study](https://blog.cloudflare.com/scaling-out-postgresql-for-cloudflare-analytics-using-citusdb/)
* [MixRank](https://mixrank.com/) uses Citus to efficiently collect
and analyze vast amounts of data to allow inside B2B sales teams
to find new customers. [Case
Study](https://www.citusdata.com/solutions/case-studies/mixrank-case-study)
* [Neustar](https://www.neustar.biz/) builds and maintains scalable
ad-tech infrastructure that counts billions of events per day using
Citus and HyperLogLog.
* [Agari](https://www.agari.com/) uses Citus to secure more than
85 percent of U.S. consumer emails on two 6-8 TB clusters. [Case
Study](https://www.citusdata.com/solutions/case-studies/agari-case-study)
* [Heap](https://heapanalytics.com/) uses Citus to run dynamic
funnel, segmentation, and cohort queries across billions of users
and tens of billions of events. [Watch
Video](https://www.youtube.com/watch?v=NVl9_6J1G60&list=PLixnExCn6lRpP10ZlpJwx6AuU3XIgNWpL)

___

Copyright © 2012–2016 Citus Data, Inc.

[faq]: https://www.citusdata.com/frequently-asked-questions
[linux_install]: https://www.digitalocean.com/community/tutorials/how-to-install-and-use-docker-compose-on-ubuntu-14-04
[mac_install]: https://www.docker.com/products/docker-toolbox
[tutorial]: http://docs.citusdata.com/en/v5.1/tutorials/tut-hash-distribution.html