What is Client in SAP

Client
Introduction
 
A client is a self-contained business entity or unit within each SAP system with independent information and data. The main objective of the client is to keep the business data isolated so that other clients cannot access or change them.

The SAP client concept allows an organization to split a system into logical subunits. Clients may operate as separate business units, where all data is stored in a common database. Client specific data includes User Master Records (including authorizations and user groups), data customization and application/business data

• Client-specific data is data affecting only one client, such as user master and application data.
• Cross-client data is data affecting the whole system environment, such as cross-client Customizing data and all Repository objects.

SAP supports up to 1000 clients starting from 000 to 999.

SAP Standard Clients 

SAP R3 comes with 3 inbuilt standard clients,

000 – Master Client aka Reference Client

Client 000 contains a simple organizational structure of a test company and includes parameters for all applications, standard settings, and configurations for the control of standard transactions and
examples to be used in many different profiles of the business applications. It contains clien independent settings.
 

001 – Copy of Client 000
This client is a copy of the 000 client including the test company. This client's settings are  clientindependent if it is configured or customized. People normally use 001 client to create a new client.

066 – EarlyWatch Client (SAP Support)
The SAP EarlyWatch Alert is a diagnosis service, for solution monitoring of SAP and non-SAP systems in the SAP Solution Manager. Alert may contain Performance issue, average response time, current system load, Database administration etc.

Golden Client
Golden Client is the client where all the developments i.e. changes and modifications like configuration settings and cross-client customizations are made and tested, which are later transported to the Quality and Production clients.

A Golden client is configured to automatically record all changes and store in change requests.

SAP Work Process and Types

Work Processes

The SAP work process is a component of the application server that executes an ABAP application.
SAP work processes are started as operating system processes, each with its own process ID (PID).
The majority of the processing of the application is performed by the SAP work processes.

D – Dialog
V – Update
E – Enqueue
B – Background
M – Message Server
S – Spool
G – Gateway Server

Dialogue

It is the only work process which communicates interactively with the users.
There should be at least 2 Dialogue work process per instance. Dialogue work process initiates Update, Background and Spool.The dialog work processes are in charge of the interactive tasks of the R/3 system. A dialog work process performs the dispatcher in the request queues after user input are assigned to the next free work process. The dialog work processes execute just one single dialog step at a time and become immediately free for the next user request (dialog step), which is assigned by the dispatcher. This is called work process multiplexing. This means that the dialog work processes can be constantly switching between different user sessions. This type of processing allows a great deal of resource distribution; otherwise the system would need as many dialog work processes as the number of expected interactive users.  It works exactly the same as multiuser operating systems. Depending on the type of business transactions the users are working on, a dialog work process can support from 5 to more than 10 simultaneous users each. This means that 10 dialog work processescould theoretically support approximately 100 users. However, this is just a rule of thumb. Tuning this parameter means that if users have to wait long to get a free work process, you should increase the parameter.

Update

It is used to update the transactions in the database. It is initiated by Dialogue process. There should be at least 1 Update work process in the entire system. It is also recommended to have an update process for every 5 Dialogue.

Enqueue

It is used to provide locks for the records that are going to be updated. It ensures consistency for updates. There will be only 1 Enqueue configured in the system during the installation. It is possible to have more than one enqueue provided they are installed or configured on the central instance.

Background

The tasks which are expensive or time consuming are scheduled to run in the background mode noninteractively. There should be at least 2 background work process in the system

Message

There should be only 1 message server in me entire R/3 system. It is used to manage all the dispatchers. It is used to load balance the requests to identity the least loaded dispatcher. It is also used to provide locks to the request that are coming from Dialogue instances.
Gateway

It is used to provide a means of communication with SAP and NON-SAP systems. There will be only 1 gateway for each instance.

Spool

It is used to print the documents to a printer or output to a fax machine etc. There should be at least 1 Spool process in the entire system. It is also possible to configure more spool process depending on the print/spool volume.

Sybase sybctrl: connect to DB fails error

Symptom

On Linux / Unix sybctrl cannot connect to database.
The error message is similar to:
Could not load SYB library libsybdrvodb.so. No database connection possible.
Other Terms

sybctrl sybxctrl
 
Reason and Prerequisites

If sybctrl has the s-bit set and runs as a setuid program, LD_LIBRARY_PATH will be ignored by operation system for security reasons.
Shared libraries will not to be found and load of odbc driver will fail.
 
Solution

Use sybxctrl which is a copy of sybctrl without the s-bit set.

sybxctrl will be created if the database is stopped using stopsap script or stopdb script.

Otherwise create sybxctrl by executing as user adm:
 
cd /usr/sap//SYS/exe/run
 
cp sybctrl sybxctrl




More details refere Snote : 2719763