The application layer of AS ABAP can be distributed on multiple application servers. If an AS ABAP has multiple application servers, they are usually instantiated on different computers. However, multiple application servers for one or more AS ABAPs can also be instantiated on the same host. Transaction SM51 displays an overview of the application servers of the current AS ABAP and their instantiated computers. The network name of the computer where the current application server is located can be obtained from the system field sy-host in the ABAP program.
The following figure is a screenshot of the SM51 transaction code of the ABAP server logged in by the author:
User Session
Logging in to the application server opens a user session. Login using SAP GUI, RFC interface or ICF (including APC). A user session is allocated its own user memory area where SPA/GPA parameters can be stored. When executing an ABAP program, there are various types of user sessions and various rules that apply:
- Dialog sessions
- Background sessions
- Update sessions
- RFC sessions
- ICF sessions
- APC sessions
Each application server has access to the central AS ABAP database. Each application server has its own shared memory. The ABAP runtime environment uses shared memory for programs, program data, and buffers (for example, in SAP buffers). ABAP programs can store shared objects and data clusters in shared memory.
From a user session, more user sessions can be opened on the same application server or another server in a program-driven fashion. E.g:
- A remote function call with target 'NONE' opens a user session on the same application server.
- Invoking an update module with COMMIT WORK or executing an executable program in background programming opens a separate user session.
- ICF clients and APC clients can open new user sessions by addressing the current application server or another server as an ICF server or APC server.
Use the configuration file parameter rdisp/tm_max_noto configure the maximum number of user sessions. The configuration file parameter rdisp/rfc_max_login determines the percentage of sessions that can be opened using the RFC interface.