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Coordination of access to one-phase commit and two-phase commit capable resources in the same transaction

Last participant support enables the use of a single one-phase commit capable resource with any number of two-phase commit capable resources in the same global transaction. We can have multiple interactions that involve the one-phase commit resource in the same transaction, but only one such resource can be involved.

At transaction commit, the two-phase commit resources are prepared first using the two-phase commit protocol, and if this is successful, the one-phase commit-resource is then called to commit. The two-phase commit resources are then committed or rolled back, depending on the response of the one-phase commit resource.

If the global transaction is distributed across multiple application servers that are all running at WebSphere Application Server version 6.1 or later, we can exploit last participant support to coordinate a one-phase commit capable resource and any number of two-phase commit capable resources in the same transaction, in a limited number of scenarios.

Last participant support introduces an increased risk of an heuristic outcome to the transaction. That is, the transaction manager cannot be sure that all resources were completed in the same direction (either committed or rolled back). For this reason, to enable an application to coordinate access to one-phase and two-phase commit capable resources in the same transaction, we configure the application to accept the heuristic hazard, that is, accept the increased risk of an heuristic outcome.

An heuristic outcome occurs if the transaction service (JTS) receives no response from the commit one-phase flow on the one-phase commit resource. In this situation, the transaction service cannot determine whether changes for the one-phase commit resource were committed or rolled back, so cannot drive reliably the correct outcome of the global transaction on the other two-phase commit resources.

We can configure the transaction service for an application server to accept the heuristic hazard, or we can configure applications individually to accept the heuristic hazard. We can configure applications individually either when they are assembled, or after they are deployed.

We can configure the transaction service for an application server to indicate whether or not to log that it is about to commit the one-phase commit resource. This does not reduce the heuristic hazard, but ensures any failure, and subsequent recovery, of the application server during the one-phase commit phase occurs with knowledge of whether or not the one-phase commit resource was asked to commit:


Transaction exceptions that involve both one-phase and two-phase commit resources

The exceptions that can be thrown by transactions that involve one-phase and two-phase commit resources are the same as those that can be thrown by transactions involving only two-phase commit resources.

The exceptions that can occur are listed in the API reference information in the WAS information center.


Subtopics

  • Additional Application Programming Interfaces (APIs)