topic Re: luw in Application Development and Automation Discussions

luw

Former Member — Mon, 28 May 2007 07:10:19 GMT

what is the diff b/w sap luw and db luw?

plz explain me in simple terms instead of sending me the links

Re: luw

Former Member — Mon, 28 May 2007 07:11:00 GMT

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:

• 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.

• 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.

• 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 doesn’t 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.

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Regards

Anji

Re: luw

Former Member — Mon, 28 May 2007 07:12:58 GMT

Hi,

Database (LUW)

A database LUW is the mechanism used by the database to ensure that its data is always consistent.

SAP (LUW)

An SAP LUW is a logical unit consisting of dialog steps, whose changes are written to the database in a single database LUW.

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Thanks

Aneesh

Re: luw

Former Member — Mon, 28 May 2007 07:13:48 GMT

Hi,

1.SAP LUW----COMMIT AT THE END OF TRANSACTION

2.DB LUW------COMMIT AFTER EVERY SCREEN

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

LUW AND ITS TYPES CAN BE OBTAINED FROM THE LINKS GIVEN

http://help.sap.com/saphelp_nw04/helpdata/en/41/7af4bca79e11d1950f0000e82de14a/content.htm

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

Regards,

Priyanka.

Re: luw

Former Member — Mon, 28 May 2007 07:16:37 GMT

Hi,

go thru this link:

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

Regards

Shiva

Re: luw

Former Member — Mon, 28 May 2007 07:17:08 GMT

Hi,

Database LUW is a series or sequence of inseperable database operations which ends with a database commit.as mentioned these database perations cannot be seperated into individula steps or tasks.The database LUW is either fully executed by the database system or not at all.

SAP 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. If an SAP LUW contains database changes, you should either write all of them or none at all to the database. To ensure that this happens, you must include a database commit when your transaction has ended successfully, and a database rollback in case the program detects an error.

I think u are clear with the reply.

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Rgds,

Prajith

Re: luw

Former Member — Mon, 28 May 2007 08:53:54 GMT

Hi,

Are you clear with the above explanation? Have you read any documentation on the LUW concept?

Let me try to simplify:

Dialog step: End of PAI(current screen) and Begining of PBO(next screen)

DB LUW: Is control by system where implicit commit work or rollback work will be automatically trigger by system at end of every dialog step.

SAP LUW: Where we can control the commit work/rollback work at the end of a transaction(could be the last screen of a transaction. this is base on your design).

For eg, 1st screen is to key in the Header info, and 2nd screen is to key in the Item Info. By using SAP LUW, we bundle the DB updating when reach the COMMIT WORK command at the 2nd screen.

The purpose for SAP LUW is to avoid inconsistency of DB updating. Let take the above eg, if we don't use SAP LUW - bundling concept of update we will face the inconsistency bet. Header and Item data if the DB updating fail at the Item update.

Meaning this is the DB LUW type, because end of 1st screen system will update the header data to table implicitly(automatically without our notice), when it comes to 2nd screen eventhough the item data has failed but there is no way for us to perform the rollback for the Header data that we have updated at 1st screen..

But when we use bundling, we place those DB updating code in a FM. Where we call the FM in program as CALL FM xxx IN UPDATE TASK. We place the FM xxA into 1st screen, and FM xxB into 2nd screen. Bear in mind, FM xxA and xxB will only be executed when it reaches the explicit COMMIT WORK command in 2nd screen. And please put message type A in the FMs if the DB updating fails. Once the updating fails, system will auto rollback all the updating included 1st and 2nd screen. For this we can ensure the consistency if 2nd screen fail, 1st screen's update will never carry out as well.

Please code a sample dialog program for this, and debug into it. You will get better understanding.

Please let me know if there is problem.

Hope it helps.