Two-Phase Commit

Two-Phase Commit

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Two-Phase Commit (2PC) is a distributed algorithm used to ensure atomicity and consistency of transactions that span multiple resources or systems. It ensures that all participating resources agree to commit or abort a transaction in a coordinated manner.

Here’s how the Two-Phase Commit process works:

  1. Coordinator: The transaction coordinator is responsible for coordinating the commit or abort decision among the participating resources. It initiates the transaction and sends a prepare request to all participants.
  2. Voting Phase: In this phase, each participating resource, known as a participant, receives the prepare request from the coordinator. The participant checks if it can successfully commit the transaction based on its own state and constraints. If it can, it votes “Yes” to the coordinator; otherwise, it votes “No”.
  3. Decision Phase: Based on the votes received from participants, the coordinator determines the final decision for the transaction. If all participants voted “Yes,” the coordinator sends a commit request to all participants. If any participant voted “No,” the coordinator sends an abort request to all participants.
  4. Commit or Abort: Upon receiving the commit or abort request, each participant performs the corresponding action. If it receives a commit request, it makes the transaction permanent by applying the changes to its resources. If it receives an abort request, it rolls back any changes made during the transaction.

The Two-Phase Commit protocol ensures that all participants agree on the outcome of the transaction. If any participant fails or does not respond during the protocol, the coordinator can take appropriate measures to recover the transaction and ensure consistency.

Two-Phase Commit provides a reliable mechanism for coordinating distributed transactions, ensuring that either all participating resources commit the transaction or none of them do. It guarantees atomicity and consistency but may introduce some blocking during the commit phase, making it important to handle failures and timeouts properly to avoid potential issues in distributed systems.

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