Loosely-coupled and tightly-coupled modes

The database server supports XA global transactions in loosely coupled and tightly coupled modes:
  • Loosely coupled mode means that the different database servers coordinate transactions, but do not share resources. The records from all branches of the transactions display as separate transactions in the logical log.
  • Tightly coupled mode means that the different database servers coordinate transactions and share resources such as locking and logging. The records from all branches of the transactions display as a single transaction in the logical log.

The Tuxedo Transaction Manager, provided by BEA systems, supports loosely coupled mode. Tuxedo operates on both UNIX and Windows.

Windows only: The MTS/XA Transaction Manager, which operates only on Windows, supports the tightly coupled mode. MTS tightly coupled transaction support on the database server includes:
  • Support for application programs with two tiers (a business-logic layer and a data-access layer).
  • Connection pooling and session pooling.

MTS tightly coupled transaction support does not affect existing loosely coupled-transaction support. The same database server can use both loosely coupled and tightly coupled transaction support at the same time.

MTS tightly coupled transaction support has the following restrictions:
  • Temporary tables are limited to one transaction branch. Different transaction branches within one global transaction cannot share a temporary table.
  • Different transaction branches within one global transaction cannot share cursors.
  • Different transaction branches within one global transaction cannot share an isolation level or lock-wait mode. The isolation level and lock-wait mode of each transaction branch must be set individually or set to the default level. If you want the same isolation level for all transaction branches, you must use SQL to specify this information for each transaction branch.

For a complete list of supported transaction managers, contact your marketing representative.


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