Pathway/XM System Management Manual

Configuring Servers
Compaq NonStop™ Pathway/XM System Management Manual—426761-001
6-4
Defining the Server-Class Type
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The files that your server program recognizes by the names ORDERS and PARTS
are the files $DATA.REG1.ORDFILE and $DATA.REG2.PARTFILE, respectively.
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When the PATHMON process starts a server process, it transmits the following
PARAM message:
SWITCH-1 “ON”
Defining the Server-Class Type
The TYPE attribute determines the way in which Pathway/XM manages the server
processes within the server class. Each server class can be defined as DISTRIBUTED,
REPLICATED, or DIRECT. If you omit this attribute, the default is DISTRIBUTED.
Distributed Server Classes
Server classes of type DISTRIBUTED can take maximum advantage of the load-
balancing features of the Pathway/XM environment.
For distributed server classes, the Pathway/XM environment uses process reservations
rather than links to manage requests for access to server processes. A process
reservation is the assignment of a server process to an LCS, which processes its queue
for a specified period of time.
The link control service (LCS) processes balance the workload of transaction requests to
distributed server classes on a per-transaction basis. Requests from TCPs and
LINKMON processes to distributed server classes are routed to an LCS process for that
server class under a particular PATHMON process. The LCS process acts as a proxy
server for its server class; it controls the request queue for the server class, requests
server-process reservations from the process broker (PB) process on behalf of the
requesters, and forwards requests to the server processes.
You can temporarily reconfigure many attributes of distributed server classes online,
while your application is running, by using the PXMCOM CONTROL SERVER
command. For details on how to do this, see Reconfiguring Distributed Server Classes
Online on page 9-5.
Distributed server classes do not support context-sensitive Pathsend servers; therefore,
you must define server classes for such servers as replicated or direct server classes.
Distributed server classes do not support named singleton servers (server classes that
consist of a single, named server process) or servers that run as process pairs. You must
define such servers as direct server classes.
It is also recommended that if your server classes are not managed by the Transaction
Management Facility (TMF), you define them as either replicated or direct server
classes. If you define such server classes as distributed, you must provide your own
mechanism for transaction recovery if the LCS process fails. If your server’s
transactions are not managed by TMF and the LCS process fails after the server has
completed processing the transaction, but before the LCS could reply to the requester,
the server processes could still be running and the data modified by the server is in
doubt.