SAP BASIS NOTES -3

Application Server:


Instance:  Instance is an application server which provides various services

We have 2 types of instance:
1)    Central instance
2)    Application instance

Instance is defined by set of services ie D,E,V,B,G,M,S

Central instance:
1)    This is an instance where all the services are configured  ( ie D,E,V,B,G,M,S)
2)    This is identified by message work process
3)    Generally message and enque will be hosted on same instance

Application Instance:
1)    AI is an additional layer of R/3 architecture i.e., user for reducing the load from directly falling on central instance.
2)    There in no DB in an application instance.

NOTE: the server in which DB is present is referred as DB server or central instance.  We can divide Application Server into two parts

For set of software components to work together we need a set of work process

Presentation Layer                           Application Layer                  Database Layer
Gui web browser                                 D, E, V, B, G, M, S                       DB 
gui for win html

•    We have seven types of work process in application layer
•    Each work process can be configured in a particular instance or server
•    The  no of work process which can be configured in instance is 0-99
•    If we need to configured more then 100 process (i.e 101) we need a new instance   
•    Each work process will have one dispatcher
•    Dispatcher is called  as waiting queue

Dispatcher:  There will be one dispatcher for an instance
•    Dispatcher is user to handle a request
•    Dispatcher receives a request and kept them in queue till that particular work process is free
•    Dispatcher follows FIFO  method
•    Dispatcher can be monitored from OS level by command DPMON
•    Dispatcher runs by an executable file Disp+Work.exe  located in run directory
•    The profile parameter to display the no of work process is  rdisp/wp_no_<type of wp>
Ex;-     Dialog = rdisp/wp_no_<dia> = 0-99
Background= rdisp/wp_no_<B+C> = 0-99
Spool = rdisp/wp_no_<spool> = 0-99

Work process:-


1) Dialog : the instance in which they are Max no of dialog work process is called as dialog instance
Note: For an instance to work we need a minimum of two dialog work process

2) Enque: The instance in which they are Max no of Enquee work process is called as Enquee instance
 Note:  Enquee work process are used for locking and unlock of sap objects in a table
             We should have minimum of one enquee work process in an instance
             (By default we have one work process)

3) Background: The instance in which they are Max no of back ground work process is called as background instance
Note: This work process is user for handling the jobs which are scheduled in the background
Ex: - Jobs like list of financial accounting Data, profit and loss sheet, Production related info etc……
Note: Jobs are of three types
1)    Medium :
2)    High
3)    Low:
These are represent by different colors as well as monitored and administrated by using third party tools

4) Update work process: this is of two types
1)    Primary update (v) : task critical activities  are primary update
2)    Secondary update (v1) : non critical activities are secondary update
Note: Max no of job are of secondary update type

5) Gateway:  gateway is used for communication between 2 SAP R/3 system
Note: Between SAP R/3 system and non SAP and between R/3 to R/2
          Gateway work process is used  for external communications
          Minimum of one work process is needed

6) Spool: is used for handling request to external devices like printers and fax machines
Note: A minimum one spool work process is required

7)Message: They are three functions of message work process
   •  Handling the input request from the presentation layer
   •  Communication with dispatcher and the work process
   •  Logon load balancing

Note:
  We will always have only one message work process in any R/3 installation.
•  The server in which M + enquee work process available that server is called central instance or central server.
•   The servers in which other type of work process available except message(ie D,E,V,B,G,S) such server is called as application server or application instance
•  The transaction code to monitor the type of  servers or  instance is SM51
•  In SM51 we can see only active servers or instances
•  The transaction code to monitor both active and inactive instance is SM66
•  SM66 is also called as global process overview
•  Transaction code to monitor the list of work process present  in particular SM50
•  Each work process required around 75 to 115 MB of memory to be configured
•  We can set the execution time for each and every work process by using profile parameters
•  Default execution time for a work process is 60 sec



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