# ScyllaDB — NoSQL Data Store Compatible with Cassandra

> ScyllaDB is a high-performance NoSQL database built on the Seastar framework. Drop-in compatible with Apache Cassandra and Amazon DynamoDB APIs but 10x faster thanks to its shard-per-core, shared-nothing architecture written in C++.

## Install

Save in your project root:

## Quick Use

```bash
# Docker (single node)
docker run -d --name scylla -p 9042:9042 scylladb/scylla:latest \
  --smp 2 --memory 2G --overprovisioned 1

# CQL shell
docker exec -it scylla cqlsh
```

CQL (Cassandra Query Language — fully compatible):
```sql
CREATE KEYSPACE tokrepo WITH replication = {
  "class": "NetworkTopologyStrategy",
  "datacenter1": 3
};

USE tokrepo;

CREATE TABLE assets (
  id uuid PRIMARY KEY,
  repo text,
  stars int,
  tags set<text>,
  created_at timestamp
);

INSERT INTO assets (id, repo, stars, tags, created_at) VALUES
  (uuid(), "react", 230000, { "frontend", "ui" }, toTimestamp(now()));

SELECT * FROM assets;
SELECT * FROM assets WHERE stars > 100000 ALLOW FILTERING;

CREATE INDEX ON assets (repo);
```

## Intro

ScyllaDB is a distributed, wide-column NoSQL database that is drop-in compatible with Apache Cassandra (CQL protocol) and Amazon DynamoDB (via Scylla Alternator), but delivers 10x the throughput. Written in C++ on the Seastar framework with a shard-per-core, shared-nothing architecture and userspace network stack. Used at Discord, Expedia, Comcast, and Epic Games.

- **Repo**: https://github.com/scylladb/scylladb
- **Stars**: 15K+
- **Language**: C++
- **License**: AGPLv3 (Open Source) / commercial (Enterprise)

## What ScyllaDB Does

- **CQL compatibility** — drop-in for Cassandra
- **DynamoDB compatibility** — via Alternator
- **Shard-per-core** — one thread per CPU core, no lock contention
- **User-space I/O** — bypass kernel for networking and storage
- **Workload prioritization** — classify and prioritize queries
- **Incremental compaction** — avoid disk space amplification
- **Materialized views** — auto-maintained denormalized tables
- **LWT (lightweight transactions)** — Paxos-based linearizable operations
- **Change Data Capture** — stream CDC events

## Architecture

Built on Seastar (userspace C++ framework). Each CPU core owns a shard of data with no shared state — eliminating lock contention and context switching. Userspace TCP stack (DPDK optional) and direct I/O to disk.

## Self-Hosting

```yaml
# 3-node cluster
version: "3"
services:
  scylla-node1:
    image: scylladb/scylla:latest
    command: --seeds=scylla-node1 --smp 4 --memory 8G
  scylla-node2:
    image: scylladb/scylla:latest
    command: --seeds=scylla-node1 --smp 4 --memory 8G
  scylla-node3:
    image: scylladb/scylla:latest
    command: --seeds=scylla-node1 --smp 4 --memory 8G
```

## Key Features

- Cassandra + DynamoDB wire compatibility
- Shard-per-core architecture
- Sub-millisecond P99 latency
- Linear scaling
- Workload prioritization
- Incremental compaction
- Materialized views
- Change Data Capture
- ScyllaDB Manager for ops
- ScyllaDB Monitoring Stack

## Comparison

| Database | Protocol | Architecture | Language |
|---|---|---|---|
| ScyllaDB | CQL + DynamoDB | Shard-per-core | C++ |
| Cassandra | CQL | JVM threads | Java |
| DynamoDB | DynamoDB API | Managed | Proprietary |
| HBase | Custom | Region servers | Java |
| Redis Cluster | RESP | Shard per node | C |

## 常见问题 FAQ

**Q: 真的比 Cassandra 快 10x？**
A: 在特定 benchmark 下是的。核心差异：C++ 无 GC、shard-per-core 无锁、userspace I/O。实际收益视工作负载而定。

**Q: 迁移 Cassandra 难吗？**
A: 不难。CQL 协议和驱动兼容，数据格式相同。大部分项目几小时可迁移。

**Q: AGPLv3 限制？**
A: 修改源码后如作为网络服务提供需开源改动部分。自用、嵌入应用不受影响。商业版有专业 support + 企业功能。

## 来源与致谢 Sources

- Docs: https://docs.scylladb.com
- GitHub: https://github.com/scylladb/scylladb
- License: AGPLv3

---
Source: https://tokrepo.com/en/workflows/0114254d-35f7-11f1-9bc6-00163e2b0d79
Author: AI Open Source