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