SAP with Microsoft SQL Server 2005: Best Practices for High Availability, Maximum Performance, and Scalability23
Central services. Central services include Batch Scheduling, Memory Services, and Enqueue Services.
Data persistence layer. Each VM has a data persistence layer that operates on different schemas within the SAP database. Shared transactions (database transactions) cannot be performed between the ABAP and Java VMs.
Message server. This server is the communication port for the SAP CI. The message server handles all communication with other instances within the same system. It also handles the initial communication to establish a client session with the Dispatcher of an instance.
For more information, see “SAP NetWeaver: Providing the Foundation to Enable and Manage Change” at .
SAP NetWeaver Application Server with Windows
In contrast to products such as SQL Server 2005 that are developed on a Windows platform, SAP NetWeaver Application Server is a multiprocess application, not a multithread application.
SAP processes that are configurable within one SAP NetWeaver Application Server instance include:
Dialog process. This process allows user interaction to move from the Presentation tier to the Application tier. Normally, there are multiple processes offering dialog services in each instance.
Update process. SAP processes execute asynchronous changes on the database. There must be one update process for each system. There can be instances without an update process.
Batch process. This process handles long-running, noninteractive jobs in the background. SAP product tasks can be scheduled to run at a certain point in time or when an event occurs.
Enqueue process. This process handles SAP logical locking management. There must be at least one Enqueue process for each SAP system. This process runs only on the SAP Central Instance.
In some cases, when there is a gap between a user confirmation and the end of an asynchronous update, a SAP object such as the Material or Customer object must be locked before the database is accessed. In these cases, the Enqueue process handles the locking and unlocking of requests on the SAP NetWeaver Application Server Layer system-wide. Database locks could harm concurrency on the database. The Enqueue process keeps the database from being flooded with locks and it blocks objects not yet released.
Spool process. This process enables print services for a SAP system. The process sends a print request to the Windows spool manager.
Message server process. This process allows for communication between the different NetWeaver Application Server instances within one SAP system. The message server runs on the SAP CI.
Gateway process. This process is responsible for external communication between NetWeaver Application Servers.
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