Pathway/XM System Management Manual

Configuring Servers
Compaq NonStop™ Pathway/XM System Management Manual—426761-001
6-5
Defining Server Groups
Direct and Replicated Server Classes
Direct and replicated server classes allow you to use 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.
Direct server classes are comparable to the server classes defined by NonStop™ TS/MP.
These server classes are managed by the well-known named PATHMON process–that
is, the one PATHMON process in the Pathway/XM environment that is defined with an
externally known name. When multiple PATHMON processes are created within the
Pathway/XM environment, a direct server class operates as an associative server under
each additional PATHMON process.
Named singleton servers (server classes that consist of a single, named server process)
and servers that run as process pairs must be defined as direct server classes.
Replicated server classes are similar to direct server classes, but are managed by their
local PATHMON processes rather than being defined as associative servers. When
multiple PATHMON processes are created within the Pathway/XM environment, such a
server class is replicated under each PATHMON process.
Server classes that use context-sensitive Pathsend servers must be defined as either
direct or replicated server classes.
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. No
LCS processes are associated with these server classes. The PB processes assign server
processes to CPUs when the server class is started with a PXMCOM START SERVER
command, and these assignments remain the same for the life of the server class.
As a result, load balancing of direct and replicated server processes is static, rather than
dynamic as it is for distributed server processes. When processor workload changes, the
PB can shift distributed server processes to the more lightly loaded processors, taking
into account the fixed locations of direct and replicated servers.
To maximize the advantages of the Pathway/XM environment, is recommended that you
define all server classes as type DISTRIBUTED if they are capable of running as
distributed server classes. Those that cannot run as distributed server classes should be
defined as type REPLICATED, if possible. In most cases, only those that cannot run as
distributed or replicated server classes should be defined as type DIRECT.
If you have server classes that handle a relatively low transaction workload, you might
also want to define such server classes as DIRECT. Doing so reduces the resource
requirements for those server classes and increases the resources available for the more
high-volume server classes in your environment.
Defining Server Groups
The GROUP attribute allows you to define a group of server classes to be referred to by
a single name. If you have defined server-class groups in your configuration, you can