Distributed Transactions

In a distributed database system, transactions often need to access data spread across multiple sites. To handle this, each site has a local transaction manager and a transaction coordinator, each with specific roles:

Local Transaction Manager

• Purpose: Manages individual transactions at the site level.
• Responsibilities:
  • Maintaining a Log: Keeps a log of all transactions for recovery purposes. This ensures that, in case of failure, data can be restored to a consistent state.
  • Coordinating Concurrent Transactions: Manages the concurrent execution of transactions to prevent issues like deadlock or inconsistent data. This includes controlling access to resources and ensuring isolation between transactions.

Transaction Coordinator

• Purpose: Manages the overall execution of distributed transactions.
• Responsibilities:
  • Starting Transactions: Initiates the distributed transaction and assigns tasks to the appropriate sites based on where the necessary data is located.
  • Distributing Subtransactions: Breaks down the main transaction into subtransactions and assigns each subtransaction to the site where its data is located.
  • Coordinating Termination: Ensures that each transaction finishes correctly. This involves coordinating with all involved sites to commit (if all are successful) or rollback (if there is an error at any site), ensuring data consistency across the distributed system.