SAP Instance
An instance is a unit of an SAP system, a set of work processes and shared memory running on an application server, administered as one. Understanding instances is key to how SAP scales and how it is operated.
An SAP instance is one running copy of the application-server software: a dispatcher, its dialog, background, update, enqueue and spool work processes, and memory buffers. A system has a central services instance for message and enqueue, a primary application server and as many additional instances as capacity needs, all on one database; Basis tunes work-process counts and memory.
- Watch out: Confusing instance, system and client.
What an instance is
An instance is one running copy of the SAP application-server software: its dispatcher, its work processes (dialog, background, update, enqueue, spool) and its memory buffers. A system can have one instance or many, all connected to the same database.
Central and dialog instances
- A central services / ASCS instance provides message and enqueue services.
- The primary application server instance.
- Additional application server instances for more capacity.
Instances and scaling
You scale an SAP system horizontally by adding application-server instances, distributing user load across them via the message server. Each instance adds work processes and memory, increasing how many users and jobs the system can handle, while all share one database.
Operating instances
Basis administrators start, stop, monitor and tune instances, adjusting work-process counts and memory to the workload. Instance configuration (the ratio of dialog to background processes, for example) directly affects performance.
Common pitfalls
- Confusing instance, system and client.
- Poor work-process ratios per instance.
- Assuming a single instance in production designs.