Pathway/XM System Management Manual

Overview of Configuring and Managing Pathway/XM

Compaq NonStop™ Pathway/XM System Management Manual—426761-001

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Server Classes and Server Processes

A server class is a group of processes that provide services to requesters, such as

SCREEN COBOL requester programs (running as terminal tasks) or Pathsend

requesters. Processes in a server class typically perform a specific type of application

work (for example, adding customer names and addresses, calculating invoice totals, or

checking inventory).

All processes within a server class run copies of the same server program, which means

that all processes within a server class provide the same set of functions. This

replication of server-class function allows you to distribute the transaction workload

across multiple processors in a system.

The number of server processes in a server class can vary. It is usually determined by

application response-time requirements and the transaction workload. Additional server

processes can be created during peak workloads to maintain acceptable throughput.

A server class can be defined as a distributed server class, taking maximum advantage of

the features of the Pathway/XM environment, or as a direct or replicated server class.

The latter two types of server class are provided for backward compatibility with

existing servers that were coded to depend on the process-management and link-

management mechanisms used by NonStop™ TS/MP and Compaq NonStop™

Pathway/iTS without Pathway/XM. These server-class types allow you to migrate your

applications more gradually to the Pathway/XM environment.

Requests to distributed server classes are handled by the link control service (LCS) and

process broker (PB) processes in the Pathway/XM environment. Requests to direct and

replicated server classes are managed directly by the TCP, PATHMON, and (for

Pathsend requests) LINKMON processes, using the link-management mechanisms of

the NonStop™ TS/MP and Pathway/iTS products; the LCS and PB processes are

bypassed. As a result, the workload of direct and replicated server classes is balanced at

server-class startup only, not dynamically as it is for distributed server classes.

Many configuration attributes of distributed server classes can be changed online, while

your application is running, by using PXMCOM commands.

LINKMON Processes and Pathsend Requesters

A LINKMON process is a multitasking process that handles the interface between

Pathsend requesters and Pathway server classes.

Each processor (CPU) in a Compaq NonStop™ Himalaya has one LINKMON process,

which starts when the CPU starts. The LINKMON process is shared by all Pathsend

requesters running in a given CPU. LINKMON processes facilitate communication

between Pathsend requesters and their servers, much as TCP and PATHMON processes

provide those functions for SCREEN COBOL requesters.

Pathsend requesters (also called Pathsend processes) are self-contained processes that

use Pathsend procedure calls to access Pathway server classes; they do not use or require

the presence of a TCP. Such requesters are written in languages such as C, C++,

COBOL85, or the portable Transaction Application Language (pTAL).