about LUW

[Former Member]

Hi experts,

any body please tell me what is LUW and what is need of it inABAP pro

[Former Member]

This message was moderated.

[Former Member]

Hi,

Please check the following standard sap help

http://help.sap.com/saphelp_47x200/helpdata/en/41/7af4bfa79e11d1950f0000e82de14a/content.htm

Thanks

Naren

[Former Member]

Hi Mahesh,

A Logical Unit of Work (LUW or database transaction) is an inseparable sequence of database operations which must be executed either in its entirety or not at all. For the database system, it thus constitutes a unit.

LUWs help to guarantee database integrity. When an LUW has been successfully concluded, the database is once again in a correct state. If, however, an error occurs within an LUW, all database changes made since the beginning of the LUW are canceled and the database is then in the same state as before the LUW started.

An LUW begins

o each time you start a transaction

o when the database changes of the previous LUW have been confirmed (database commit) or

o when the database changes of the previous LUW have been cancelled (database rollback)

An LUW ends

o when the database changes have been confirmed (database commit) or

o when the database changes have been canceled (database rollback)

SAP memory and ABAP memoryUsing SAP memory. User-specific memory retained for the duration of the session. Can only be used for simple field values.

Using ABAP memory. Can be used to transfer data between internal modi. Can be used to transfer any ABAP/4 variables ( Fields, strings, internal tables, complex objects)

SAP memoryYou use the SPA/GPA parameters to pass data. These paramters are saved globally in memory. The paramters are indetified by a three-character code.

In dialog programs you can SET and GET these parameters in the attribute window of the screen field, by marking the SET and GET fields and put the name of the parameter in the ParameterId field.

In a program ( Dialog or Report ) you can use the GET PARAMETER and SET PARAMETER statements:

set parameter id 'RV1' field <fieldname>

get parameter id 'RV1' field <fieldname>

also check this link

http://help.sap.com/saphelp_nw04/helpdata/en/41/7af4bfa79e11d1950f0000e82de14a/content.htm

Regards,

KK

[Former Member]

Hi Mahesh.

Check this SDN link.

Also if you search with keyword LUW you will the same there are quite a few which starts with LUW,

Will provide you the answer.

Also.

http://help.sap.com/saphelp_47x200/helpdata/en/41/7af4bfa79e11d1950f0000e82de14a/content.htm

LUW: A logical unit consisting of dialog steps, whose changes are written to the database in a single database LUW is called an SAP LUW. Unlike a database LUW, an SAP LUW can span several dialog steps, and be executed using a series of different work processes.

Mohinder Singh

[Former Member]

Hi mahesh,

[http://www.auditmypc.com/acronym/LUW.asp]

Regards,

Sravanthi

[Former Member]

Hi Mahesh,

Go through this link.

Regards.

Eshwar.

[Former Member]

Hi mahesh,

The R/3 system is multi user system and many users access the same information at the same time, which is mainly DATA. Consider the case where one user is modifying a record, and second user is trying to delete the same record. If the second user is successful in deleting the record then the first user will face problem for modifying the record that is already deleted. The avoid such situation, R/3 system has provided Logical Unit of Work, which is defined as a locking mechanism to protect transaction integrity. Of course, there are other measures, which ensures data integrity like check table i.e. foreign key relationship. Within SAP system there are three types of transaction and may be distinguished as:

u2022 Database transaction known as LUW. It can be defined as a period in which operation requested must be performed as a unit, i.e. all or nothing operation. At the end of LUW, either of the database changes are committed or rolled back.

u2022 Update transaction or SAP LUW. One SAP LUW can have several databases LUW. So a set of a database is either committed or rolled back. The special ABAP/4 command COMMIT WORK, marks the end of a SAP LUW.

u2022 ABAP/4 transaction. Is made up of a set of related task combined under one transaction code. ABAP/4 transactions are for programming environment, in which ABAP/4 transaction functions like one complete object containing screens, menus and transaction codes.

R/3 system has provided in built locking mechanism, which defines the Logical Unit of Work. Also user can set his own locking mechanism. The LUW starts when a lock entry in the system table is created, and it ends when the lock is released.

To provide the user the facility to communicate with the table in order to modify or delete or insert data, R/3 has provided tool called SCREEN PAINTER. This tool allows you to design screen, process screen through program and update the database table. SAP has provided one and only one way to update the database table, i.e. transaction. Though you can update database table by using open SQL statement through program, SAP usually doesnu2019t recommend this kind of updating. Many standard transactions are available to update standard table but if the need arises, the developer should be able to develop new transaction, which allows the updating of database tables. This can be achieved by using various components of screen painter.

With thanks & regards,

Sravani yendru.

[Former Member]

This message was moderated.

[Former Member]

Hi,

<copy_and_paste_removed_by_moderator>

Rewards points if helpful. <= You are about to be deleted!!!

cheers,

sowjanya

Edited by: Julius Bussche on Jul 24, 2008 3:12 PM

[Former Member]

Hi,

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 SAP System, database commits and rollbacks can be triggered either implicitly or using explicit commands.

Implicit Database Commits

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:

· When a dialog step is completed

Control changes from the work process back to the SAP GUI.

· When a function module is called in another work process (RFC).

Control passes to the other work process.

· When the called function module (RFC) in the other work process ends.

Control returns to the calling work process.

· When a WAIT statement interrupts the work process.

Control passes to another work process.

· Error dialogs (information, warning, or error messages) in dialog steps.

Control passes from the work process to the SAP GUI.

Explicit Database Commits

There are two ways to trigger an explicit database commit in your application programs:

· Call the function module DB_COMMIT

The sole task of this function module is to start a database commit.

· Use the ABAP statement COMMIT WORK

This statement starts a database commit, but also performs other tasks (refer to the keyword documentation for COMMIT WORK).

Implicit Database Rollbacks

The following cases lead to an implicit database rollback:

· Runtime error in an application program

This occurs whenever an application program has to terminate because of an unforeseen situation (for example, trying to divide by zero).

· Termination message

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

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 ROLLBACK WORK).

From the above, we can draw up the following list of points at which database LUWs begin and end.

A Database LUW Begins

· Each time a dialog step starts (when the dialog step is sent to the work process).

· Whenever the previous database LUW ends in a database commit.

· Whenever the previous database LUW ends in a database rollback.

A Database LUW Ends

· Each time a database commit occurs. This writes all of the changes to the database.

· Each time a database rollback occurs. This reverses all of the changes made during the LUW.

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 SAP Locking Concept).

Reward Points if useful

Raghunath.S

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