Global Transactions

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	DB2 Universal Database for OS/390 v7.1 Application Certification Guide By Susan Lawson
	Table of Contents
	Chapter 7.  Application Program Features

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Global Transactions

Global transactions allow for several UOWs to share locks if they are all participants in a unit of work. The larger unit of work is referred to as a global transaction. This provides a way to avoid deadlocks between transactions. There are several reasons that you may want to consider combining several transactions into a large transaction. For example, this may be an option if you are adding OO (object-oriented) interfaces on existing transactions.

This simply is an extension of the distributed unit of work and adds the ability to share locks. It supports IMS, RRS (Recoverable Resource Services), and DDF (Distributed Data Facility) transactions. These transactions will be identified via a tokenglobal transaction ID or XID. All of the URs in a global transaction must run on the same subsystem, and each part can see uncommitted updates of other parts .

The sharing of locks is limited to normal transaction locks and an explicit LOCK TABLE statement, or partition key updates could still cause deadlocks or timeouts. There are many design issues to consider prior to the use of global transactions, and there are also additional risks and exposures.

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