# Xandra

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> Fast, simple, and robust Cassandra driver for Elixir.

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Xandra is a [Cassandra][cassandra] driver built natively in Elixir and focused on speed, simplicity, and robustness.
This driver works exclusively with the Cassandra Query Language v3 (CQL3) and the native protocol versions 3 and 4.

## Features

This library is in its early stages when it comes to features, but we're already [successfully using it in production at Forza Football][production-use]. Currently, the supported features are:

  * connection pooling with reconnections in case of connection loss
  * prepared queries (with local cache of prepared queries on a per-connection basis) and batch queries
  * page streaming
  * compression
  * clustering (random and priority load balancing for now) with support for autodiscovery of nodes in the cluster (same datacenter only for now)
  * customizable retry strategies for failed queries
  * user-defined types
  * authentication
  * SSL encryption

See [the documentation][documentation] for detailed explanation of how the supported features work.

## Installation

Add the `:xandra` dependency to your `mix.exs` file:

def deps() do
  [{:xandra, "~> 0.11"}]

Then, run `mix deps.get` in your shell to fetch the new dependency.

## Overview

The documentation is available [on HexDocs][documentation].

Connections or pool of connections can be started with `Xandra.start_link/1`:

{:ok, conn} = Xandra.start_link(nodes: [""])

This connection can be used to perform all operations against the Cassandra server.

Executing simple queries looks like this:

statement = "INSERT INTO users (name, postcode) VALUES ('Priam', 67100)"
{:ok, %Xandra.Void{}} = Xandra.execute(conn, statement, _params = [])

Preparing and executing a query:

with {:ok, prepared} <- Xandra.prepare(conn, "SELECT * FROM users WHERE name = ?"),
     {:ok, %Xandra.Page{}} <- Xandra.execute(conn, prepared, [_name = "Priam"]),
     do: Enum.to_list(page)

Xandra supports streaming pages:

prepared = Xandra.prepare!(conn, "SELECT * FROM subscriptions WHERE topic = :topic")
page_stream = Xandra.stream_pages!(conn, prepared, _params = [], page_size: 1_000)

# This is going to execute the prepared query every time a new page is needed:
|> Enum.take(10)
|> Enum.each(fn page -> IO.puts("Got a bunch of rows: #{inspect(Enum.to_list(page))}") end)

## Scylla support

Xandra supports [Scylla][scylladb] (version `2.x`) without the need to do anything in particular.

## Contributing

To run tests, you will need [Docker][docker] installed on your machine. This repository uses [`docker-compose`][docker-compose] to run multiple Cassandra instances in parallel on different ports to test different features (such as authentication or SSL encryption). To run normal tests, do this from the root of the project:

docker-compose up -d
mix test

The `-d` flags runs the instances as daemons in the background. Give it a minute between starting the services and running `mix test` since Cassandra takes a while to start. To stop the services, run `docker-compose stop`.

To run tests for Scylla, you'll need a different set of services and a different test task:

docker-compose --file docker-compose.scylladb.yml up -d
mix test.scylladb

Use `docker-compose --file docker-compose.scylladb.yml stop` to stop Scylla when done.

By default, tests run for native protocol v3 except for a few specific tests that run
on native protocol v4. If you want to test the whole suite on native protocol v4, use:


## License

Xandra is released under the ISC license, see the [LICENSE](LICENSE) file.