9.4.1.2 Two-phase Commit Protocol
When the tpcommit() function is called, it initiates the two-phase commit protocol. This protocol, as the name suggests, consists of two steps:
- Each participating resource manager indicates a readiness to commit.
- The initiator of the transaction gives permission to commit to each participating resource manager.
The commit sequence begins when the transaction initiator calls the tpcommit() function. The Oracle Tuxedo TMS server process in the designated coordinator group contacts the TMS in each participant group that is to perform the first phase of the commit protocol. The TMS in each group then instructs the resource manager (RM) in that group to commit using the XA protocol that is defined for communications between the Transaction Managers and RMs. The RM writes, to stable storage, the states of the transaction before and after the commit sequence, and indicates success or failure to the TMS. The TMS then passes the response back to the coordinating TMS.
When the coordinating TMS has received a success indication from all groups, it logs a statement to the effect that a transaction is being committed and sends second-phase commit notifications to all participant groups. The RM in each group then finalizes the transaction updates.
If the coordinator TMS is notified of a first-phase commit failure from any group, or if it fails to receive a reply from any group, it sends a rollback notification to each RM and the RMs back out all transaction updates. tpcommit() then fails and sets tperrno(5) to TPEABORT.