Special Edition Using SAP R/3, Third Edition

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Special Edition Using SAP R/3, Third Edition - CH 3 - Exploring R/3 Architecture Page 16 of 26 If a data element is declared as a U1 primary update component, it always is assigned by the dispatcher to a primary work process, where it is given high priority. Primary components take precedence over secondary components. Primary update components are usually time-critical control data elements that must be recorded in the database as soon as possible. Seat reservations and changes to the records of material available for immediate production are examples. The primary components of different log records can be assigned to different update processes and updated concurrently. Secondary Update Components (U2) The secondary components in a log record of a transaction have to wait until all the primary components are processed. The secondary components then can be dealt with in any order--if necessary, by different update processes, perhaps running on different computers. U2 secondary components carry the data for results and statistical returns that do not need to be updated immediately. The dispatcher assigns these components in work packets for the work processes as these resources become available. Error States During Updating The dialog process under control of the dynamic programs catches errors--such as values outside the permitted range--before the transaction is accepted from the user. Problems in the updating process are more likely to occur for technical reasons, such as the overflow of a file or database buffer. These error conditions are routed automatically to the system administrator, who deals with these problems. Data Consistency If a technical error occurs during database updating, it cannot be corrected by the user. Any changes already proposed by the update component are rejected, and the entire update component is refused. If the component refused is a U1 primary component, all the associated primary components in the same log record are reversed, and the entire log record is excluded from the update process. By contrast, if a U2 secondary update component is unacceptable, only that component is blocked. Notification of Rejected Database Updates A rejected update component is assigned an identifier that generates a standard message for automatic transmission to the user whose dialog caused the faulty log or whose update was rejected for some other reason. This message is processed by the SAPmail component of SAPoffice and can be sent to any user of an SAP application who has the mail facility enabled. Multiprocessor Environments The inherent client/server design of the R/3 system lends itself to the employment of multiprocessors. Different work processes can be run on separate processors and on processors of different types. The file://J:\prodinfo\MEMBERS\MA\ir057.html 3/23/01
Special Edition Using SAP R/3, Third Edition - CH 3 - Exploring R/3 Architecture Page 17 of 26 development of hardware and operating systems can provide enhancements to the operation of the R/3 system without the need for reprogramming or extensive reconfiguring. System Management If the backbone and nerve center of your organization is an R/3 application, you need and expect continuous operation, perhaps over a wide geographical complex working 24 hours a day. The CCMS-Computing Center Management System is discussed in Chapter 11, "Maintaining the Computer System." In particular, you expect the system to do much of its work in the form of background processes from which you can demand reports at any time and in any convenient format. Several types of work can be done in the background, and each is given a system designed to optimize the activities. Dialog-Free Background Processing With a user in the loop, the R/3 system uses the online dialog programs to call for input and to check its validity before submitting it for further processing. Background processes frequently use the same programs that control the dialogs. Any number of background processes can be executed along with the online dialogs. Spooling Control The scope of spooling techniques includes all forms of buffered relay of information to media such as printers and fax devices. Many computers can be involved. It is usual to designate one computer as the spool server through which all spooling jobs are routed to and from the spooling systems of the individual computers. If a new device is added to the network, it has to be defined only once to the server. A central file is designated as temporary sequential (TEMSE) to buffer the information to be output to the spooling mechanism. For each TEMSE dataset, a separate order contains detailed instructions that include the logical name of the destination printer or other device. Enqueue Central Lock Management The locking mechanisms of many relational database systems are not adequate to control complex business data objects. To meet this need for controlling access from many users and applications to a complex data object, the parts of which may be distributed among any number of relational tables, the R/3 system uses an internal central lock manager installed on one of the database servers or on one of the application servers. When a transaction consists of several dialog steps, the dispatcher can assign each step to a different work process. It is essential that no changes are made to any data object that has been locked until all the dialog steps are completed. The locks assigned have to be transferred when work processes are changed. If a database operation is to be uncoupled from a dialog process, it is also essential that certain data file://J:\prodinfo\MEMBERS\MA\ir057.html 3/23/01
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Special Edition Using SAP R/3, Third Edition

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