How do distributed transactions work (2PC, Saga pattern)?

Two-Phase Commit (2PC): coordinator sends prepare to all participants; if all vote yes, sends commit, else abort. Guarantees atomicity but blocking and slow. Saga pattern: sequence of local transactions with compensating transactions for rollback. Choreography (events) or orchestration (central coordinator). Eventual consistency, no distributed locks. 2PC for strong consistency (traditional databases), Saga for microservices and long-running transactions. Consider Paxos/Raft for consensus.