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

Last participant support (LPS) 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. You 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.

Note: If the global transaction is distributed across multiple application servers that are all running at WebSphere Application Server version 5.1 or later, you can exploit last participant support to coordinate a one-phase commit capable resource and any number of two-phase commit capable resources within 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 within the same transaction, you configure the application to accept the increased risk of an heuristic outcome.

[Fix Pack 17 or later] Alternatively, you can configure the transaction service for an application server to accept the increased risk of an heuristic outcome. In this way, last participant support is enabled for all applications that run on that server.

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.

You 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 that 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:



Related tasks
[Fix Pack 17 or later] Configuring last participant support for an application server
Configuring transaction properties for an application server
Using one-phase and two-phase commit resources in the same transaction
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Last updatedLast updated: Aug 31, 2013 12:02:36 AM CDT
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