Two-phase commit protocol

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In a “normal execution” of any single distributed transaction ( i.e., when no failure occurs, which is typically the most frequent situation), the protocol consists of two phases:

  1. The commit-request phase (or voting phase), in which a coordinator process attempts to prepare all the transaction’s participating processes (named participants, cohorts, or workers) to take the necessary steps for either committing or aborting the transaction and to vote, either “Yes”: commit (if the transaction participant’s local portion execution has ended properly), or “No”: abort (if a problem has been detected with the local portion), and
  2. The commit phase, in which, based on voting of the cohorts, the coordinator decides whether to commit (only if all have voted “Yes”) or abort the transaction (otherwise), and notifies the result to all the cohorts. The cohorts then follow with the needed actions (commit or abort) with their local transactional resources (also called recoverable resources; e.g., database data) and their respective portions in the transaction’s other output (if applicable).