Database Logical Unit of Work (LUW)
From the point of view of database programming, a database LUW is an inseparable sequence of database operations that ends with a database commit. The database LUW is either fully executed by the database system or not at all. Once a database LUW has been successfully executed, the database will be in a consistent state. If an error occurs within a database LUW, all of the database changes since the beginning of the database LUW are reversed. This leaves the database in the state it was in before the transaction started.
The database changes that occur within a database LUW are not actually written to the database until after the database commit. Until this happens, you can use a database rollback to reverse the changes. In the R/3 System, database commits and rollbacks can be triggered either implicitly or using explicit commands.
Implicit Database Commits in the R/3 System
A work process can only execute a single database LUW. The consequence of this is that a work process must always end a database LUW when it finishes its work for a user or an external call. Work processes trigger an implicit database commit in the following situations:
Control changes from the work process back to the SAP GUI.
Control passes to the other work process.
Control returns to the calling work process.
Control passes to another work process.
Control passes from the work process to the SAP GUI.
Explicit Database Commits in the R/3 System
There are two ways to trigger an explicit database commit in your application programs:
The sole task of this function module is to start a database commit.
This statement starts a database commit, but also performs other tasks (refer to the keyword documentation for COMMIT WORK).
Implicit Database Rollbacks in the R/3 System
The following cases lead to an implicit database rollback:
This occurs whenever an application program has to terminate because of an unforeseen situation (for example, trying to divide by zero).
Termination messages are generated using the ABAP statement MESSAGE with the message type A or X. In certain cases (updates), they are also generated with message types I, W, and E. These messages end the current application program.
Explicit Database Rollbacks in the R/3 System
You can trigger a database rollback explicitly using the ABAP statement ROLLBACK WORK. This statement starts a database rollback, but also performs other tasks (refer to the keyword documentation for COMMIT WORK).
From the above, we can draw up the following list of points at which database LUWs begin and end.
A Database LUW Begins
A Database LUW Ends
Database LUWs and Database Locks
As well as the database changes made within it, a database LUW also consists of database locks. The database system uses locks to ensure that two or more users cannot change the same data simultaneously, since this could lead to inconsistent data being written to the database. A database lock can only be active for the duration of a database LUW. They are automatically released when the database LUW ends. In order to program SAP LUWs, we need a lock mechanism within the R/3 System that allows us to create locks with a longer lifetime (refer to
The R/3 Locking Concept).