Two-phase commit

Q: How deeply does PostgreSQL Mistakes and How to Avoid Them cover two-phase commit?

Defines the prepare-and-decision protocol and operational hazards, but does not provide a complete implementation procedure.

As explained in PostgreSQL Mistakes and How to Avoid Them

Two-phase commit is a distributed transaction protocol in which participants first prepare to commit and then commit or abort based on a coordinator decision.

Two-phase commit (2PC) coordinates an atomic transaction across database nodes: participants prepare first, then commit or abort according to the coordinator’s decision. PostgreSQL can protect each local transaction while an application still violates atomicity across nodes. section 5.6

The split account update

Suppose alpha debits an account from 100 to 90 while beta applies a gift and records 150. The business loses 10 while the customer receives an unintended 50: local ACID guarantees did not make the cross-node operation atomic. PREPARE TRANSACTION and its associated commands provide the two-phase mechanism, but prepared transactions should remain short-lived. section 5.6

Treat 2PC as a constrained operational tool:

Expect latency and replication lag to complicate prepared transactions. section 5.6
Run prepared transactions exclusively on the primary, potentially eliminating read-replica benefits. section 5.6
Clean up incomplete transactions because they retain locks and may delay applications after crashes or restarts. section 5.6

How PostgreSQL Mistakes and How to Avoid Them covers it

Cover of PostgreSQL Mistakes and How to Avoid Them

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Also explained in

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Think Distributed SystemsA distributed transaction commit protocol that coordinates commitment in two phases among participating processes.
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Kafka for ArchitectsTwo-phase commit is a distributed transaction protocol in which a coordinator first prepares all participants and then directs them to commit or abort as a group.
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Amazon Web Services in Action, Third Edition: An in-depth guide to AWSTwo-phase commit is a distributed transaction protocol that first obtains participant decisions and then instructs all participants to commit if every participant agrees.

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Related concepts

protocolkind of · A protocol is a defined set of rules and conventions governing communication or interaction among systems, components, or participants.
livenessaddresses · Liveness is a correctness property requiring that a system eventually makes specified progress or produces a desired event or condition.
Apache Kafkaused by · Apache Kafka is a distributed event-streaming platform for publishing, storing, processing, and consuming streams of records.
distributed transactionuses · A distributed transaction is a unit of work whose operations span multiple resources or systems and whose outcome is coordinated across them.

This explainer was generated by Manning's knowledge graph from the text of PostgreSQL Mistakes and How to Avoid Them. The section links point to the parts of the book it draws on.