Note: This library is under active development and the API may change.

AshScylla

An Ash Framework data layer for ScyllaDB/Apache Cassandra

Quick Start • Features • Documentation • Contributing • License

Overview

AshScylla enables you to use ScyllaDB or Apache Cassandra as a persistence layer for your Ash Framework resources. It implements the Ash.DataLayer behaviour using Xandra (a native Elixir CQL driver) to communicate via CQL (Cassandra Query Language).

Current version: 0.13.1

Key Benefits

• Seamless Ash Integration: Use familiar Ash resources, actions, and queries
• ScyllaDB Performance: Leverage ScyllaDB's high-performance, low-latency architecture
• Cassandra Compatibility: Works with Apache Cassandra and ScyllaDB
• Rich Feature Set: TTL, consistency levels, secondary indexes, materialized views, batch operations, lightweight transactions

Quick Start

Prerequisites

• Elixir 1.17+
• Running ScyllaDB or Cassandra instance
• Basic knowledge of Ash Framework

Installation

Add ash_scylla to your dependencies in mix.exs:

def deps do
  [
    {:ash_scylla, "~> 0.13"}
  ]
end

Minimal Setup

# 1. Configure a Repo
defmodule MyApp.Repo do
  use AshScylla.Repo, otp_app: :my_app
end

# 2. Configure in config/config.exs
config :my_app, MyApp.Repo,
  nodes: ["127.0.0.1:9042"],
  keyspace: "my_app_dev",
  pool_size: 10

# 3. Add to your supervision tree
# lib/my_app/application.ex
children = [MyApp.Repo, ...]

# 4. Create a resource
defmodule MyApp.User do
  use Ash.Resource,
    data_layer: AshScylla.DataLayer,
    domain: MyApp.Domain


  scylla do
    table "users"
    consistency :quorum
  end

  attributes do
    uuid_primary_key :id
    attribute :name, :string
    attribute :email, :string
  end

  actions do
    defaults [:create, :read, :update, :destroy]
  end
end

# 5. Create a Domain
defmodule MyApp.Domain do
  use Ash.Domain

  resources do
    resource MyApp.User
  end
end

# 6. Create keyspace and run migrations
# mix ash_scylla.setup
# mix ash_scylla.migrate

# 7. Use it
{:ok, user} = Ash.create(MyApp.User, %{name: "John", email: "john@example.com"})
users = MyApp.User |> Ash.read!()

For a complete step-by-step guide, see the Usage Guide.

Features

Core Ash Features

| Select | ✅ | Select specific fields | | Multitenancy | ✅ | Keyspace-based multitenancy | | Bulk Create | ✅ | Batch INSERT operations | | Upsert | ✅ | INSERT with lightweight transactions (LWT) | | Update Query | ✅ | Bulk update via filtered queries | | Destroy Query | ✅ | Bulk delete via filtered queries | | Distinct | ✅ | DISTINCT on partition key columns | | Calculate | ✅ | In-memory calculations | | Aggregate (count) | ✅ | Per-partition COUNT |

ScyllaDB-Specific Features

Configuration

Resource Configuration

defmodule MyApp.User do
  use Ash.Resource,
    data_layer: AshScylla.DataLayer,
    domain: MyApp.Domain


  scylla do
    table "users"
    consistency :quorum
    ttl 3600
    lwt true

    secondary_index :email
    secondary_index [:name, :age]

    materialized_view :users_by_email,
      primary_key: [:email, :id],
      include_columns: [:name, :age]

    per_action_consistency read: :one, create: :quorum
  end
end

Repo Configuration

# Single-node
config :my_app, MyApp.Repo,
  nodes: ["127.0.0.1:9042"],
  keyspace: "my_app_dev"

# Multi-node cluster (all nodes must use the same port)
config :my_app, MyApp.Repo,
  nodes: ["scylla-1:9042", "scylla-2:9042", "scylla-3:9042"],
  keyspace: "my_app_prod",
  pool_size: 50

Pool Size Formula:pool_size = num_nodes * num_cores_per_node

Limitations

Observability

Telemetry

AshScylla emits standard :telemetry events for all query and batch operations:

:telemetry.attach(
  "ash_scylla-logger",
  [:ash_scylla, :query, :stop],
  &MyApp.Telemetry.handle_event/4,
  nil
)

Events:[:ash_scylla, :query, :start|stop|exception], [:ash_scylla, :batch, :start|stop]

Prepared Statement Caching

children = [
  AshScylla.PreparedStatementCache,
  # ...
]

Documentation

Common Commands

# ── Testing ──────────────────────────────────────────────────────────────────
mix test --exclude integration              # Unit tests only (no database)
mix test --only integration                 # Integration tests (needs ScyllaDB)
SCYLLA_DIRECT=1 mix test --only integration # Integration tests against local DB
mix test test/integration/cluster_integration_test.exs --only integration  # Cluster tests
mix test --exclude integration --cover      # Unit tests + coverage report

# ── Code Quality ─────────────────────────────────────────────────────────────
mix format --check-formatted                # Check formatting
mix credo --strict                          # Static analysis
mix dialyzer                                # Type checking
mix quality                                 # All three above

# ── Benchmarks ───────────────────────────────────────────────────────────────
mix run benchmarks/run_benchmarks.exs

# ── Database ─────────────────────────────────────────────────────────────────
mix ash_scylla.setup                        # Create keyspace
mix ash_scylla.migrate                      # Run all migrations
mix ash_scylla.migrate --schemas-only       # Run only schema files
mix ash_scylla.migrate --resource MyApp.User # Run migrations for one resource
mix ash_scylla.gen --dev                    # Generate schema migration from DSL

# ── Schema Generation ────────────────────────────────────────────────────────
mix ash_scylla.generate_migrations           # Generate CQL from Ash resource DSL

# ── Ash Extension Callbacks ──────────────────────────────────────────────────
mix ash.install AshScylla --resource MyApp.User  # Install for a resource
mix ash.reset AshScylla                           # Reset database
mix ash.rollback AshScylla --version 20240101     # Rollback (logs warning)
mix ash.tear_down AshScylla                       # Drop keyspace

Contributing

Contributions are welcome!

1. Fork the repository
2. Clone your fork
3. Create a feature branch: git checkout -b feature/my-feature
4. Make your changes
5. Run tests: mix test --exclude integration
6. Check quality: mix quality
7. Commit and push
8. Open a Pull Request

Development Setup

mix deps.get
podman-compose -f podman-compose.yml up -d
mix test

A .devcontainer/devcontainer.json is provided for VS Code Dev Containers.

License

This project is licensed under the Apache License 2.0 - see the LICENSE file for details.

Acknowledgments

• Ash Framework - The Elixir framework this data layer integrates with
• Xandra - Native Elixir CQL driver for ScyllaDB/Cassandra
• ScyllaDB - High-performance NoSQL database

Made with ❤️ for the Elixir and Ash communities