What is an SAP Instance?

An instance is a unit that can (and has to) be started and stopped as a whole. It is made up of several OS Processes, memory areas used by individual process and shared by all the processes, and files.

Primary and Additional Application Servers

The business logic is executed in an SAP instance. It can be an ABAP instance (logic is executed by work processes) or Java instance (logic is executed by application threads in a server node)

An SAP system can be made up of several such instances. The first instance is called Primary Application Server (it used to be called Central Instance). Instances after PAS, that can execute business logic, are called Additional Application Servers (it used to be called as Dialog Instances)

Central Services

To keep track of which instance is up and is least loaded, SAP uses a Message Server. So if a logon is made via Message Server, it checks which instance is least used and logs the user on to that server. You can group the type of users, provide them a logon group, and assign a set of instances to a logon group for a higher degree of control.

When a business user is executing a transaction, it would be making changes to several tables. To ensure that the records that are being changed by one transaction is not changed by any other transaction, a lock is placed on the record. The locks on tables, or even other objects are handled by an Enqueue Service.

Message Service and the Enqueue Service are both part of SAP Central Services. ABAP systems have their own central services instance - ASCS and for Java systems have central services instances as SCS.

ASCS and SCS also control SAP licensing. An SAP system can have only one central services instance. They are the central node of a star network topology.

Database Instance

All the change made by PAS and AAS are persisted to database. The DB has a set of services clubbed together to form a Database Instance.

Comments

Post a Comment

Popular posts from this blog

OS/DB Migration - CMD. STR, TOC, EXT, R3load, DDLDBS.TPL and more

Image
With increasing need to improve performance or reduce costs or vanishing support for operating systems/databases it becomes inevitable to migrate to a better OS or DB. We feel take a quick look at the primary ingredients of the tools for OS/DB migration handled by R3SETUP. Tools - R3load, R3ldctl and R3szchk R3ldctl creates STRucture files, TemPLate files by reading the technical settings for table/indexes in SAP data dictionary. R3szchk calculates the database size object sizes (EXTent files) for the target system based on the STR files created by R3ldctl. The EXT and STR files can be later split into smaller groups. The most crucial tool R3load is responsible for unloading and loading data from the database. R3load uses the files created by R3ldctl and R3szchk and dumps the data into compressed binary format as .001, .002 .. files. It uses cmd files to achieve the task. If the cmd files are not present, it creates on its own. Files Command files*.cmd  are creat...
Read more

Fixing Inconsistent Table - Table activation fails due to inconsistency between DD and DB

If you find a table to be available on the database, but not active in ABAP dictionary, try calling SE14 as DDIC user, enter the table name and choose Table > Reconstruct, Execute. If this method fails follow these steps: Call transaction code SE37 and execute the function module  DD_TABL_ACTM with single test On the next screen, do not change any other field except the following and set them as shown below: MODE: 12 NTAB_PUTSTATE: N TABNAME: <enter the correct table name> Click on Execute The export parameter ACT_RESULT should show 0. To verify if the inconsistency is fixed, call transaction SE14 > Extras > Database Object > Check and  SE14 > Extras > Runtime object > Check.
Read more

301 Redirect Using SAP Web Dispatcher

301 redirects are typically used to redirect accesses that include www to non-www or vice-versa. Example, when you call http://blogger.com, the call is redirected to www.blogger.com. An end-user may prefer to call a URL in any manner. You must ensure that all these calls are redirected to relevant URLs with content. SAP web dispatcher can be configured to send a redirect (301) to the client. To enable redirection add icm/HTTP/redirect_<xx> to the web dispatcher's profile file. The parameter uses the following syntax: icm/HTTP/redirect_<xx> = PREFIX=<URL prefix>[, FROM=<pattern for URL>, FROMPROT=<incoming protocol>, FOR=<pattern for host name:port>,TO=<new URL prefix>, PROT=<protocol>, HOST=<host>, PORT=<port number/name>] Let's say you want to redirect all the HTTP requests on mysource.com on 80 port to mytarget.com on HTTPS 443 port icm/HTTP/redirect_0 = PREFIX=/, FROM=*, FROMPROT=http, FOR=mysource.com:80,...
Read more