# Apache ShardingSphere — Distributed Database Middleware Ecosystem

> A guide to Apache ShardingSphere, the distributed database middleware that provides data sharding, read-write splitting, encryption, and shadow database capabilities.

## Install

Save as a script file and run:

# Apache ShardingSphere — Distributed Database Middleware Ecosystem

## Quick Use
```bash
# Option A: ShardingSphere-Proxy (standalone proxy)
wget https://archive.apache.org/dist/shardingsphere/5.5.0/apache-shardingsphere-5.5.0-shardingsphere-proxy-bin.tar.gz
tar -zxvf apache-shardingsphere-5.5.0-shardingsphere-proxy-bin.tar.gz
cd apache-shardingsphere-5.5.0-shardingsphere-proxy-bin
# Edit conf/server.yaml and conf/config-sharding.yaml
sh bin/start.sh
# Connect via MySQL client on port 3307
mysql -h 127.0.0.1 -P 3307 -u root -p
```

## Introduction
Apache ShardingSphere is a distributed database middleware ecosystem that transforms any database into a distributed database system. It provides data sharding, read-write splitting, data encryption, and shadow database testing without requiring application code changes, supporting MySQL, PostgreSQL, and other databases transparently.

## What ShardingSphere Does
- Shards data horizontally across multiple database instances with configurable sharding strategies
- Splits read and write traffic automatically between primary and replica databases
- Encrypts sensitive columns transparently with pluggable encryption algorithms
- Provides shadow database routing for production-environment stress testing without affecting real data
- Offers distributed transaction support via XA and BASE transaction modes

## Architecture Overview
ShardingSphere operates in two deployment modes. ShardingSphere-JDBC is a lightweight Java library that intercepts JDBC calls and routes SQL to the correct shards, running in-process with your application. ShardingSphere-Proxy is a standalone database proxy that speaks the MySQL or PostgreSQL wire protocol, acting as a transparent middleware layer. Both modes share the same sharding engine that parses SQL, rewrites queries for target shards, executes them in parallel, and merges results.

## Self-Hosting & Configuration
- Choose JDBC mode (embedded library) for Java applications or Proxy mode for any language
- Define sharding rules in YAML specifying sharding columns, algorithms, and table mappings
- Configure read-write splitting rules with primary and replica data source definitions
- Set up data encryption rules mapping logical columns to cipher columns and algorithms
- Use DistSQL (ShardingSphere DDL) to manage rules dynamically via SQL statements at runtime

## Key Features
- Pluggable sharding algorithms: hash, range, time-based, or custom strategies
- DistSQL for managing sharding, encryption, and splitting rules via SQL without config files
- Multi-database support: MySQL, PostgreSQL, openGauss, and SQL Server as backend databases
- Online schema migration for resharding data between old and new sharding configurations
- Cluster governance with ZooKeeper or etcd for distributed rule synchronization

## Comparison with Similar Tools
- **Vitess** — MySQL sharding by PlanetScale; ShardingSphere supports more databases and offers encryption and shadow DB features
- **Citus** — PostgreSQL-native sharding extension; ShardingSphere works as middleware across multiple database types
- **ProxySQL** — MySQL proxy for query routing; ShardingSphere adds sharding logic, encryption, and distributed transactions
- **MyCat** — MySQL middleware; ShardingSphere has a larger community, active Apache governance, and richer feature set
- **Native partitioning** — Database-level partitioning; ShardingSphere distributes across separate instances for true horizontal scaling

## FAQ
**Q: Should I use JDBC mode or Proxy mode?**
A: JDBC mode has lower latency (no extra network hop) and suits Java applications. Proxy mode supports any language via standard database protocols and simplifies operations.

**Q: Can ShardingSphere handle cross-shard joins?**
A: Yes, for simple joins. ShardingSphere supports cross-shard queries by fetching data from multiple shards and merging in memory. Complex joins may require binding table rules.

**Q: Does ShardingSphere support distributed transactions?**
A: Yes. It supports XA transactions (via Atomikos or Narayana) and BASE transactions (via Seata) for cross-shard consistency.

**Q: Can I migrate an existing database to ShardingSphere?**
A: Yes. The online migration feature can reshard data from a single database to a sharded topology with minimal downtime.

## Sources
- https://github.com/apache/shardingsphere
- https://shardingsphere.apache.org/document/current/en/overview/

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Source: https://tokrepo.com/en/workflows/754f7671-3d7d-11f1-9bc6-00163e2b0d79
Author: Script Depot