The Update Process
Use
Among other things, the update system is used to lighten the workload of SAP transactions when time-consuming changes are made to the database. These changes are carried out asynchronously - with only a very brief delay - by special updating work processes.
This is why the update system is widely used in SAP transactions (by almost every transaction that changes business data), although transactions can also change the data directly in the database.
Prerequisites
When developing transactions, the application programmer decides if and how the update system is used.
For more information, see the ABAP documentation Update Techniques.
Process
As the figure below shows, COMMIT WORK and the update task are called at the end of a transaction. The dialog part of the SAP transaction finishes, and the update part of the SAP LUW is started. The graphic further below displays the actions and the sequence that different work processes perform.
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After the transaction closes, the dialog work process closes the VBHDR entry (the update header of the update request), and searches for an update server for the V1 update.
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The update server distributes the tasks to an update work process. This processes the V1 modules of the update request, triggers a COMMIT to the database, and releases SAP locks held on the update request.
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Then the work process searches for an update server for the U2 update, if the U2 update modules exist.
These are forwarded from a V2 update server to a V2 work process, which processes the V2 modules, and triggers a COMMIT on the database.
The following graphic displays this process from the view of various work processes. It also displays the time at which changes to the database are made.
The V1 modules are processed by transmitting the contents of the update table VBMOD and VBDATA to the application tables of the database. The changes are actually in the desired tables in the database only at the end of the database LUW in which it occurs. The SAP locks are released and, if V2 update modules exist, the V2 update is started. This is similar to the V1 update with the exception that there are no locks that have to released and no search for a process for further processing.
Result
If the update runs without errors, the update record does not appear anymore in the update management and the data is processed.