transactions

## What I do - Manage database transactions correctly - Handle distributed transactions across services - Implement saga patterns for microservices - Optimize transaction isolation levels - Ensure data consistency ## When to use me When building systems requiring strong data consistency, distributed systems, or microservices with multiple data sources. ## Key Concepts ### ACID Properties - **Atomicity**: All or nothing - **Consistency**: Valid state to valid state - **Isolation**: Concurrent execution appears serial - **Durability**: Committed data survives failures ### Transaction Types - Implicit vs explicit transactions - Auto-commit mode - Savepoints - Nested transactions - Read-only transactions ### Isolation Levels - **READ UNCOMMITTED**: Lowest isolation, may see uncommitted data - **READ COMMITTED**: See only committed data (default in most) - **REPEATABLE READ**: Same query returns consistent results - **SERIALIZABLE**: Highest isolation, full isolation - **Snapshot Isolation**: MVCC-based isolation ### Concurrency Problems - Dirty reads - Non-repeatable reads - Phantom reads - Lost updates - Write skew ### Locking - Shared locks (S locks) - Exclusive locks (X locks) - Deadlock detection and handling - Lock escalation - Optimistic vs pessimistic locking ### Distributed Transactions - Two-phase commit (2PC) - Three-phase commit (3PC) - Saga pattern - Eventual consistency - Compensation actions - Outbox pattern ### Best Practices - Keep transactions short - Avoid long-running operations - Use appropriate isolation levels - Handle deadlocks gracefully - Test concurrency scenarios - Monitor transaction metrics