Functional Description of Updates 

The following graphic shows you how the R/3 System and the database interact when an SAP transaction is being executed, and illustrates the difference between a database LUW (Logical Unit of Work) and an SAP LUW.

The graphic shows an example of an SAP LUW. The dialog transaction extends over 3 screens. Each screen can be processed by a different (dialog) work process because while the system is waiting for the user to make an entry, the work process can be assigned a different task by the dispatcher.

The dialog transaction is completed with the statement COMMIT WORK; the update area of the LUW is then initiated: the update server (update task in the graphic) transfers the update request to an update work process. The time interval between two screen changes in the dialog transaction corresponds to a database LUW (completed with a COMMIT to DB); the update area is performed in a database LUW. The update area is described in greater detail in the section entitled The Update Process.

Database LUW vs. SAP LUW

In the case of the database, an LUW is a sequence of data operations that cannot be divided up . The operations are either carried out in full or not at all. Database LUWs are modules which go to make up the database procedures for consistent data processing. An R/3 transaction can include several database LUWs (see example above), each of which can be terminated with a database COMMIT, which is generated automatically.

By way of contrast, an LUW for the R/3 System is a business process, which cannot be divided up. The process is either executed in full or not at all. The SAP LUW of an R/3 transaction usually has to contain several database LUWs. Under normal circumstances, it contains a dialog transaction (which maps a business process), and the command for writing the data to the database (update).

In each database LUW, data is written to the database to special update tables (and not to the application tables). Once the dialog area has been completed, all of the data in a database LUW is copied to the application tables: the update request is then performed. This is described in greater detail in the section entitled The Update Process.

Advantages of the SAP Update System

The update system offers a number of advantages over database changes that are made directly in a transaction. These include:

To enhance performance even further, the application programmer can configure different types of updates (see V1 and V2 Update Modules):

See also:

Further details on the update process can be found in the following sections:

The Update Process

Distributed Processing of Updates

Main System Profile Parameters for Updates

Reporting Update Problems