SYNOPSIS

Specification for a [two-phase commit][1] protocol.

SPECIFICATION

REQUEST Phase

1. COORDINATOR

A PEER becomes a COORDINATOR when an operation is performed against it.
To achieve [atomicity][2], it will coordinate a [quorum][3]

A. Send each PEER a REQUEST packet with { data, callback-site }.

2. PEER

If a COORDINATOR is lost, the PEER will attempt to reconnect to the callback-site for a maximum of N times.
All peers must respond to the COORDINATOR

A. { data, callback-site } is written to a temporary store for [durability][4]. B. The PEERs subsequent transactions are queued to achieve [isolation][5]. C. The PEER responds to the COORDINATOR a. If yes, the PEER sends an AGREEMENT_YES response. b. If no, the PEER sends an AGREEMENT_ABORT response.

COMMIT Phase

Fail

A timed out response from a PEER is equivalent to AGREEMENT_ABORT
If any response is AGREEMENT_ABORT

A. An ABORT message is sent to all PEERs, the temporary store is purged and an ACK_FAIL response is sent to the COORDINATOR. B. ABORT is the [consistent][6] result of the transaction.

Success

If all responses are AGREEMENT_YES

A. A ACK_SUCCESS message is sent to all the PEERS so that they can commit the data that has been added to the temporary store. B. If all PEERS respond with ACK_SUCCESS C. SUCCESS is the [consistent][6] result of the transaction.