🔁 Distributed Multi-Database Transaction with Atomikos

This project demonstrates how to perform distributed transactions across multiple databases at runtime using Spring Boot, JTA, Atomikos, and a custom AbstractRoutingDataSource.

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📌 Use Case

A User belongs to a Branch, and each branch has its own separate database. When a withdrawal request is made:

• The app deletes the user from the main database.
• It looks up the DB credentials of the user’s branch from the branch_info table.
• It dynamically registers and switches to the appropriate branch database.
• It deletes the user’s wallet data (point_wallet) from the branch DB.
• All operations happen within a single distributed transaction.
• If any step fails, everything is rolled back.

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🧩 Project Structure

com.example.multitransaction
├── main                         # Main DB (User, BranchInfo)
│   └── service                  # UserService, BranchInfoService
├── branch                       # Branch DB (PointWallet)
│   └── service                  # PointWalletService
├── core                         # Withdrawal orchestration
│   └── service                  # UserWithdrawalService
├── config
│   └── db                       # Atomikos config, routing, JTA
│       ├── DatabaseContextHolder.java
│       ├── DynamicRoutingDataSource.java
│       ├── RoutingDataSourceConfig.java
│       ├── MainDbConfig.java
│       ├── BranchDbConfig.java
│       ├── BranchDatabaseService.java
│       └── JtaConfig.java
└── MultiTransactionApplication.java  # Main application class

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⚙️ Technologies Used

• Spring Boot 3+
• Spring Data JPA (Hibernate)
• Atomikos JTA Transaction Manager
• MySQL 8
• Docker & Docker Compose

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🚀 Getting Started

1. Clone the Repository

2. Build the JAR

Make sure you're using JDK 17+.

./gradlew clean build -x test

This creates the JAR at:

build/libs/multi-transaction-0.0.1-SNAPSHOT.jar

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🐳 Run with Docker Compose

docker compose up

This will spin up the following containers:

Container	Description	Port
main-db	Main database	13305
tesco-db	Branch DB (Tesco)	13306
lidl-db	Branch DB (Lidl)	13307
multi-transaction	Spring Boot API	8080

Each database is initialized using SQL files from the /init directory:

init/
├── main/
│   └── init.sql          # user, branch_info
├── tesco/
│   └── init.sql          # point_wallet
└── lidl/
    └── init.sql          # point_wallet

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🧠 Summary

• ✅ Dynamically switch to multiple databases at runtime
• ✅ Perform global transactions across databases using @Transactional
• ✅ Maintain data consistency across systems using Atomikos and XA
• ✅ Easy to extend for multi-tenant or branch-based SaaS systems