ML Wiki

Two-Phase Commit

A way to ensure consistency in a distributed system

Two Phases

Phase 1

• coordinator sends "prepare to commit" message
• subordinates make sure they can do that no matter what happens
• write the action to a Database Transaction Log to tolerate failures
• subordinates reply with "ready to commit" message

Phase 2

• if all ready, send "commit"
• if anyone fails, send "abort"

Example

1. Coordinator: update
2. Coordinator: prepare to commit
3. Subordinate: write to log
4. Subordinate: say "ready"
5. Coordinator: commit

See also

• ACID: Consistency (databases) and Durability (databases)

Sources

• Introduction to Data Science (coursera)