NOTE
2.9 Two-Stage Implementation: 2PC
A compact implementation-oriented view of two-phase commit and XA resource coordination.
This is a historical learning note and may contain outdated or incomplete understanding.
1. Two-Phase Commit
2PC coordinates multiple transactional resources through two stages:
- Prepare: every participant durably reaches a state from which it can commit if instructed.
- Decision: the transaction manager records and communicates commit or rollback.
2. Main Costs
- prepared participants can retain locks/resources while waiting;
- transaction latency includes cross-node coordination and durable logging;
- coordinator and participant recovery logic must preserve the final decision across crashes.
The important issue is not merely a “single point of failure”: a production transaction manager can itself be replicated. The hard part is safely recovering the global decision when failures occur mid-protocol.
3. XA
XA defines interfaces between the transaction manager and resource managers so multiple XA-capable databases/resources can participate in one 2PC transaction.
Use XA when the participating resource stack supports it and global atomic commit is worth the coupling and latency cost.