In this post I will be taking you into a sap R/3 system, explain you the process happening inside a SAP system. What happens between the process of pressing F8 (execute) and the displaying of result in o/p screen? Ever wondered of the operations happening inside….
There are three layers in a SAP R/3 system (3-tier architecture).
1) Presentation Layer.
2) Application Layer.
3) Database Layer.
SAP R/3 Architecture
Coming into your Presentation layer, it’s nothing but your O/P screen. Application layer is where all the logical operations take place. Database layer is where all the data is stored.
Application Layer consists of application servers (1 or more) and a message server. It also contains the work process for execution of user request.
Now coming to the working part.
As soon as you press F8 or execute a program a request is sent to the application layer. There will many requests coming to the application layer. It follows the FIFO (First in First Out) principle in considering the Request.
For executing a request a Work process is required. Application layer consists of many work processes under an application server. This process of assigning a work process based on availability is done by the Dispatcher. Following the FIFO principle, your request will be assigned a work process.
The work of message server is for load balancing. If there is multiple application servers, the message server communicate between them and assigns work simultaneously to different servers and hence reducing the load.
F8 ----------> Application layer ---------> Dispatcher ---------> Work Process (based on FIFO principle) ---------> here the work process does the work of fetching data from database layer (if required), calculations and other stuff ---------> O/p is sent to the presentation layer.
Application layer does a two way communication with database layer as well as with the presentation layer.