Two-Phase Commit Protocol Overview
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Questions and Answers

If a cohort cannot communicate with the coordinator at Step 4 of TimeOut Protocol, what should it do?

  • Block until communication is re-established. (correct)
  • Request a new coordinator from other cohorts.
  • Commit the transaction and proceed to the next step.
  • Immediately abort the transaction.

    • What is the purpose of the openSubTransaction(trans) operation in nested transactions?

  • To abort the parent transaction.
  • To check the status of a subtransaction.
  • To open a new subtransaction whose parent is `trans` and return a unique identifier. (correct)
  • To create a new subtransaction that is independent of the parent.

    • What are the possible outcomes of a transaction using the getStatus(trans) operation?

  • Completed, running, stopped.
  • Successful, failed, pending.
  • Committed, aborted, provisional. (correct)
  • Committed, aborted, provisional, in progress.

    • How does the OpenTransaction operation relate to the openSubTransaction operation in nested transactions?

    <p>The <code>OpenTransaction</code> operation creates a top-level transaction, while <code>openSubTransaction</code> creates a subtransaction under the top-level transaction. (C)</p> Signup and view all the answers

    Which of the following is a reason for blocking in a TimeOut Protocol?

    <p>A cohort cannot communicate with the coordinator. (C)</p> Signup and view all the answers

    What is the role of the coordinator in nested transactions?

    <p>To manage the commit and abort decisions for all subtransactions. (B)</p> Signup and view all the answers

    If a subtransaction aborts, what happens to its parent transaction?

    <p>The parent transaction can still commit if it's not dependent on the subtransaction. (C)</p> Signup and view all the answers

    How does a subtransaction inform its parent about its commit or abort status?

    <p>By sending a message to the parent coordinator. (C)</p> Signup and view all the answers

    Which of the following actions does a participant take after receiving a 'canCommit?' request?

    <p>The participant prepares to commit by saving objects in permanent storage. (B)</p> Signup and view all the answers

    What is the purpose of the 'getDecision' call in the Two-Phase Commit Protocol?

    <p>To allow a participant to request the decision on a transaction after it has voted 'Yes' but has not received a response from the coordinator. (D)</p> Signup and view all the answers

    In the Two-Phase Commit Protocol, what does the coordinator do if it receives at least one 'No' vote from the participants?

    <p>The coordinator sends a 'doAbort' request to all participants that voted 'Yes'. (B)</p> Signup and view all the answers

    What is the primary function of the 'haveCommitted' call in the Two-Phase Commit Protocol?

    <p>To confirm to the coordinator that a participant has successfully committed its part of the transaction. (C)</p> Signup and view all the answers

    What is the purpose of Phase 1 in the Two-Phase Commit Protocol?

    <p>To allow participants to prepare for the transaction and vote on whether to commit. (B)</p> Signup and view all the answers

    Which of the following is considered a key advantage of the Two-Phase Commit Protocol?

    <p>It ensures that all participating nodes commit to the transaction, preventing inconsistencies. (D)</p> Signup and view all the answers

    What is the main purpose of the 'canCommit?' request in the first phase of the Two-Phase Commit Protocol?

    <p>To gather votes from the participants regarding the transaction. (D)</p> Signup and view all the answers

    In the Two-Phase Commit Protocol, what happens if a participant votes 'No' in the first phase?

    <p>The participant aborts the transaction immediately. (B)</p> Signup and view all the answers

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    Flashcards

    TimeOut Protocol

    A protocol used in managing commit decisions in distributed transactions.

    Abort Decision

    A decision made when a coordinator votes for abort instead of commit.

    Blocking

    A state where a cohort cannot progress due to communication issues with the coordinator.

    Coordinator Responsibilities

    The coordinator manages communication and commit decisions for transactions.

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    Nested Transactions

    Transactions that can have subtransactions allowing hierarchical commits.

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    Provisional Commit

    An intermediate state where a transaction is tentatively committed but not finalized.

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    Transaction Identifier (TID)

    A unique identifier assigned to a top-level or subtransaction.

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    Parent-Subtransaction Relationship

    A parent transaction can commit independently of subtransactions, but their fate is linked upon abort.

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    canCommit?

    A request from the coordinator to ask if a participant can commit a transaction.

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    doCommit

    An instruction from the coordinator to a participant to commit to the transaction.

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    doAbort

    An instruction from the coordinator to a participant to abort the transaction.

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    haveCommitted

    A confirmation from the participant to the coordinator that it has committed the transaction.

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    getDecision

    A request from a participant to the coordinator for the decision on a transaction after voting Yes.

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    Voting phase

    The first phase of the Two-Phase Commit Protocol where participants cast votes on committing.

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    Completion phase

    The second phase in Two-Phase Commit, where the coordinator acts based on collected votes.

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    Transaction outcome

    The result of the voting phase in a Two-Phase Commit, either commit or abort.

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    Study Notes

    Two-Phase Commit Protocol

    • The protocol ensures atomicity in distributed transactions.
    • Two phases: voting and completion.
    • Phase 1 (Voting): Coordinator requests each participant if it can commit the transaction. Each participant confirms or rejects. If any participant rejects, the coordinator aborts immediately.
    • Phase 2 (Completion): Based on the votes, the coordinator decides to commit or abort. If all participants voted yes, it commits; otherwise, aborts. The coordinator instructs all participants to follow the decision.

    Participant Interface

    • canCommit?(trans): The coordinator queries a participant whether it can commit the transaction. The participant responds with "Yes" or "No".
    • doCommit(trans): The coordinator requests the participant to commit its part of the transaction.
    • doAbort(trans): The coordinator requests the participant to abort its part of the transaction.

    Coordinator Interface

    • haveCommitted(trans, participant): A participant notifies the coordinator that it has committed the transaction.
    • getDecision(trans): Indicates to ask the coordinator for a decision on a transaction. This is useful for recovery if the coordinator doesn't receive a response due to a crash or delay.

    Time-Out Protocol

    • If the coordinator doesn't receive a response from a participant during the voting phase, it assumes a failure and aborts the transaction.

    Nested Transactions

    • Subtransactions can be nested within a top-level transaction.
    • The transaction identifier (TID) of a subtransaction extends its parent.
    • A client finishes nested transactions by calling closeTransaction or abortTransaction.
    • The coordinator manages subtransactions, receiving commit or abort requests from them.

    Coordinator Information

    • Coordinators keep track of their subtransactions.
    • During a provisional commit, subtransactions report their state and descendants to the parent.
    • If a subtransaction aborts, it informs its parent.

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    Related Documents

    Atomic Commit Protocols PDF

    Description

    Explore the Two-Phase Commit Protocol essential for ensuring atomicity in distributed transactions. Understand the voting and completion phases, along with the interfaces for participants and coordinators involved in the transaction process. This quiz will test your knowledge on how transactions are committed or aborted based on participant responses.

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