2PC vs Saga: Atomic Commit vs Compensating Transactions

Sun, 06 Sep 2026 09:57:51 +0900

Overview

Both patterns coordinate a transaction that spans multiple services or databases, but they resolve the coordination problem in opposite ways. 2PC locks every participant until a coordinator confirms all can commit, guaranteeing atomicity at the cost of blocking; Saga lets each step commit immediately and unwinds failures afterward with compensating actions, trading strict atomicity for availability and throughput.

Comparison Diagram

Comparison Table

Aspect	2PC	Saga
Initiation	Coordinator sends a prepare request to all participants at once	First service runs its local transaction and triggers the next step
Commit decision	Coordinator waits for every vote, then issues a single atomic commit or abort	No central decision; each step commits independently as it finishes
Resource locking	Participants hold locks from prepare until the commit acknowledgment arrives	No cross-step locks; each local transaction commits and releases immediately
Failure handling	Coordinator aborts and tells all participants to roll back the uncommitted work	Already-committed steps are undone via explicit compensating transactions
Atomicity guarantee	True all-or-nothing atomicity across every participant	No real atomicity; intermediate states are visible until compensations finish
Coordination dependency	Single coordinator is a synchronous, blocking point of failure	Runs via choreography or a lightweight orchestrator that doesn’t hold locks
Latency and throughput	Higher latency and lower throughput from synchronous cross-service locking	Lower per-step latency and higher throughput since nothing blocks across services
Implementation effort	Relies on XA-compliant resources and a transaction manager	Requires custom compensating logic and step/state tracking per operation

Key Differences

2PC provides true atomicity across services, while Saga only approximates it through compensations after the fact
2PC holds locks on every participant until the coordinator commits; Saga commits each step locally with no cross-service locking
Saga failures require explicit compensating transactions; 2PC failures simply abort the still-uncommitted transaction
2PC depends on a synchronous coordinator that all participants must trust and wait on; Saga can run via choreography or a non-blocking orchestrator
2PC trades throughput for consistency, while Saga trades strict consistency for availability at scale

When to Use Each

2PC

Two-Phase-Commit on IT Comparison

2PC vs Saga: Atomic Commit vs Compensating Transactions

Overview

Comparison Diagram

Comparison Table

Key Differences

When to Use Each