Tuesday, 19 April 2016

SAP R/3 Application Server Architecture

Understanding a User Context

A user context is memory that is allocated to contain the characteristics of a user that is logged on the R/3 system. It holds information needed by R/3 about the user, such as:
  • The user’s current settings
  • The user’s authorizations
  • The names of the programs the user is currently running
When a user logs on, a user context is allocated for that logon. When they log off, it is freed. It is used during program processing, and its importance is described further in the following sections.

Understanding a Roll Area

A roll area is memory that is allocated by a work process for an instance of a program. It holds information needed by R/3 about the program’s execution, such as:
  • The values of the variables
  • The dynamic memory allocations
  • The current program pointer
Each time a user starts a program, a roll area is created for that instance of the program. If two users run the same program at the same time, two roll areas will exist-one for each user. The roll area is freed when the program ends.
NOTE
When speaking to a Basis consultant, you might hear the term roll area used to refer to all roll areas for one user or even all roll areas on one application server. You usually can determine the intended meaning from the context in which it is used.
Both the roll area and the user context play an important part in dialog step processing.

Understanding a Dialog Step

NOTE
A dialog step is used by Basis consultants as the unit of measure for system response time.
A dialog step is the processing needed to get from one screen to the next. It includes all processing that occurs after the user issues a request, up to and including the processing needed to display the next screen. For example, when the user clicks the Enter key on the Change Vendor: Initial Screen, he initiates a dialog step and the hourglass appears, preventing further input. The sapmf02k program retrieves the vendor information and displays it on the Change Vendor: Address screen, and the hourglass disappears. This marks the end of the dialog step and the user is now able to make another request.
There are four ways the user can initiate a dialog step. From the SAPGUI:
  • Press Enter.
  • Press a function key.
  • Click on a button on the screen.
  • Choose a menu item.
It is important for an ABAP/4 programmer to know about dialog steps because they form a discrete unit of processing for an ABAP/4 program.

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