11.28 Resource Managers

When you use an ATMI function to define transactions, the Oracle Tuxedo system executes an internal call to pass any global transaction information to each resource manager participating in the transaction. When you call tpcommit() or tpabort(), for example, the system makes internal calls to direct each resource manager to commit or abort the work it did on behalf of the caller’s global transaction.

When a global transaction has been initiated, either explicitly or implicitly, you must not make explicit calls to the resource manager’s transaction functions in your application code. Failure to follow this transaction rule causes indeterminate results. You can use the tpgetlev() function to determine whether a process is already in a global transaction before calling the resource manager’s transaction function.

Some resource managers allow programmers to configure certain parameters (such as the transaction consistency level) by specifying options available in the interface to the resource managers themselves. Such options are made available in two forms:

• Resource manager-specific function calls that can be used by programmers of distributed applications to configure options.
• Hard-coded options incorporated in the transaction interface supplied by the provider of the resource manager.

Consult the documentation for your resource managers for additional information.

The method of setting options varies for each resource manager. In the Oracle Tuxedo System SQL resource manager, for example, the set transaction statement is used to negotiate specific options (consistency level and access mode) for a transaction that has already been started by the Oracle Tuxedo system.