SAPSID - a three-character code such as C11, PRD, E56, etc.) SID stands for SAP System Identification. SID is a unique identification code for every R/3 installation (SAP system) consisting of a database server & several application servers. As lock management system provided by enqueue server, it will provide service to users.
Database Instance: – As normal database instance accepts requests from central instance to fulfill the user’s requests. When an instance is started, the dispatcher process attempts to establish a connection to the message server so that it can announce the services it provides (DIA, BTC, SPO, UPD, etc.).Lock table is managed in central instance by enqueue service. All dialog instances communicate with central instance before requesting database with message server. But the main thing is that it contains Enqueue and message servers. Central Instance: – Central instance can also work as dialog instance. If a number of dialog instance increases hardware resources, dispatcher, workprocesses also increases so that more number of users can login at a time. Dialog instance exists on the different host. Its purpose is to maintain the load on the server. 
Dialog Instance: – Dialog instance exists in the application layer.SAP System= Dialog Instance + Central Instance + Database Instance.įor one SAP system, all three instances share the same directory. Usually for a single application or database server within a SAP R/3 client-server environment. Sap Instance is a group of resources such as
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