topic Re: luw in Application Development and Automation Discussions

luw

Former Member — Mon, 28 May 2007 06:51:40 GMT

what is luw?

what does this mean?

plz explain me

Re: luw

Former Member — Mon, 28 May 2007 06:54:59 GMT

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

http://help.sap.com/saphelp_46c/helpdata/en/a5/3ec8654ac011d1894e0000e829fbbd/content.htm

Re: luw

Former Member — Mon, 28 May 2007 06:55:01 GMT

Hi,

There are 3 types of LUW's available in SAP

1)Database Transaction or DBLUW

2)SAP Transaction or SAPLUW

2)ABAP Transaction or ABAPLUW

1) DBLUW : when it is called it locks the rows , Update the rows & commit the rows issued by auto Commit

2) SAPLUW : collection of Business reports is called SAPLUW and Issuing the Commit

here UPDATE,INSERT,MODIFY statements are valid

Commit work is given by Developer Side.

3) ABAPLUW : What ever Transaction Code we are creating is called ABAPLUW it is belongs upon Developers

here 3 types of updates available

1) Bundled Updates

2) Un-Bundled Updates

1) Bundled Updates :

in Bundled Updates all your updates in a single unit of work present in a PERFORM 'XYZ'

PERFORM 'XYZ' on Commit.

here PERFORM-kept in Buffer 'XYZ' this form having all your update statements

Also check this link.

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

Reward if useful,

Thanks

Aneesh.

Re: luw

Former Member — Mon, 28 May 2007 06:57:34 GMT

Hi,

LUW--Logical unit of work

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)

rewards if useful

regards,

nazeer

Re: luw

Former Member — Mon, 28 May 2007 07:25:09 GMT

Hi,

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.

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)

Check this URL.

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

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

Regards,

Jackie..

Re: luw

Former Member — Mon, 28 May 2007 10:02:30 GMT

What is LUW or Data base Transaction ?

- A “LUW”(logical unit of work) is the span of time during which any database updates must be performed in an “all or nothing” manner .Either they are all performed (committed),or they are all thrown away (rolled back).In the ABAP/4 world , LUWs and

- Transactions can have several meanings:

LUW (or “database LUW” or “database transaction”)

This is the set of updates terminated by a database commit. A LUW lasts, at most, from one screen change to the next (because the SAP system triggers database commits automatically at every screen change).

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. However, since database changes from a database LUW cannot be reversed in a subsequent database LUW, you must make all of the database changes for the SAP LUW in a single database LUW. To maintain data integrity, you must bundle all of you database changes in the final database LUW of the SAP LUW

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 that make up the database procedures for consistent data processing.

By way of contrast, an LUW for the SAP System is a business process, which cannot be divided up. The process is either executed in full or not at all. An SAP LUW usually must include several database LUWs (see graphic above), each of which can be terminated with a database COMMIT, which is generated automatically. Under normal circumstances, the SAP LUW contains a dialog part (which maps a business process), and the command for writing the data to the database (update part).

In each database LUW, data is written to the database to special update tables (and not to the application tables). Once the dialog part has been completed, all of the data in a database LUW is transferred into the application tables: the update request is then performed.

Have a look at below link.

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

http://help.sap.com/saphelp_nw04s/helpdata/en/e5/de86d835cd11d3acb00000e83539c3/content.htm

Difference Between Database LUWs and SAP LUWs

To the database, an LUW is an indivisible sequence of data operations that must be completed in its entirety or not performed at all. Database LUWs are the building blocks out of which database procedures for consistent data-handling are built.

By way of contrast, an LUW for the SAP System is a business process, which cannot be divided up. The process is either executed in full or not at all. An SAP LUW must include several database LUWs (see graphic above), each of which can be terminated with a database COMMIT, which is generated automatically. Under normal circumstances, the SAP LUW contains a dialog part (which maps a business process), and the command for writing the data to the database (update part).

For each database LUW, the data is written to the database, but not to the application tables, rather to special update tables. Once the dialog part 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 updating system offers a variety of advantages over direct database changes inline in a transaction. These include:

Problems that arise as a result of different types of logical units of work (for database systems and SAP transactions) are avoided. By Bundling Updates, the update system supports critical rollback and restore functions for transactions.

● Enhanced performance for dialog transactions: time-consuming database changes are carried out asynchronously at the end of the LUW after the user has already moved onto the next LUW.

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

● Time-critical U1 updates

● Non-time-critical U2 updates, dependent on U1 updates

● Non-time-critical U2 updates that are gathered and processed at a later time (see Collective Run)

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:

· 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 in the R/3 System

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 in the R/3 System

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 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 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 R/3 Locking Concept).

Re: luw

Former Member — Mon, 28 May 2007 10:29:46 GMT

Please go through the link

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

Regards

Archana