Start the database:
· The underlying element of the entire SAP system is the database. Before the SAP instances are started, this must have operational status. The database is therefore always started as the first step.
Start the central instance:
· . Next, the operating system collector SAPOSCOL is started, if it is not already active. This is a standalone program that runs in the operating system background, independently of SAP instances. It collects data about operating system resources and makes this data available through the shared memory of all SAP instances.
· The central instance with the message server and the dispatcher and its work processes is then started. Only once the message and enqueue servers are active can other instances be started, if desired.
Start other instances:
· If the dialog instance is not running on the same host as the central instance, the SAPOSCOL operating system collector is first started on this host.
· The dispatcher is then started with its work processes.
· SAPOSCOL:Collects performance data for one or more SAP instances and runs once for each host.
· SAP<sid>_<instance no.>: Controls the SAP instances and runs once for each instance.
The specifications of the instances; that is, the type and number of processes, main memory sizes, and other options are controlled at the start of the instances using profiles. These are files at operating system level that are stored in the directory