One-phase commit global transactions with the IMS Universal drivers
If the external transaction manager detects that only one resource manager is enlisted in a given transaction, the transaction manager can perform one-phase-commit optimization.
In the one-phase-commit optimization, the first phase of the two-phase commit operation, the prepare phase, is omitted and the transaction manager sends only the commit request to the resource manager to commit the changes without first sending prepare to commit.
z/OS® Resource Recovery Services (RRS) transactions that use one-phase commit are also referred to as an RRS local transaction. Local transactions do not contain an XID.
When IMS Connect receives from the IMS Universal drivers a database access request that is an RRS local transaction, IMS Connect does not call RRS and passes the local transaction to ODBM directly. ODBM in turn calls RRS and coordinates the commit or rollback of the database request.
The following figure illustrates the flow for a distributed one-phase commit global transaction. RRS needs to be active on each z/OS image; however, IMS Connect does not need to be on the same z/OS image as ODBM and IMS.
The following figure illustrates the first 17 steps of the flow of a distributed one-phase commit global transaction that is submitted to IMS Connect from the IMS Universal drivers. The transaction involves one IMS system. RRS needs to be active on all z/OS images; however, IMS Connect does not need to be on the same z/OS image as ODBM and IMS.
The following figure illustrates the remaining steps of the flow of the distributed one-phase commit global transaction shown in the preceding figure.
