Deadlocks & Locking

Parallel transaction deadlocks are handled with four strategies: consistent lock ordering prevents cycles, optimistic locking avoids locks entirely, @Retryable auto-retries failures, and SKIP LOCKED skips busy rows for queue processing.

A @Transactional method holds a database connection for its entire duration, so a slow network call inside the transaction wastes the connection and starves other threads, causing pool exhaustion even when the database itself is healthy.