Availability Guide for Application Design

Availability in the Pathway Transaction-Processing
Environment
Availability Guide for Application Design—525637-004
6-10
Availability of Pathway/XM Server Classes
The PB processes are NonStop process pairs that manage system and CPU resource
assignments for requesters such as LCS processes and for direct server class servers.
Direct server class server processes are legacy Pathway applications that have not
been modified to take full advantage of Pathway/XM.
The LCS processes manage transaction requests to distributed server classes.
(Distributed server classes are server processes that have been converted to use the
features of Pathway/XM.) Each LCS process acts as a proxy server; it manages the
resources of its distributed server class, controls the server-class transaction queue,
and forwards requests to server processes.
The $CMON process can approve or modify the values of process startup parameters
such as the processor to run in or the priority to run with.
For more information about the Pathway/XM environment, refer to the Pathway/XM
System Management Manual.
Availability of Pathway/XM Server Classes
Pathway/XM extends the NonStop TS/MP use of replicated processes and server
classes by allowing massive scalability through the logical grouping of objects and
dynamic load-balancing for distributed server classes. Logical grouping allows for
efficient management of extremely large configurations, which improves availability by
reducing operational delays for reconfiguration or disaster recovery. Dynamic load
balancing ensures that any reduction in availability because of lost transaction-
processing capacity is minimized during disaster recovery.
When Is Recovery Action Needed?
The system and the application take recovery action under the same circumstances as
with any NonStop TS/MP environment. Refer to When Is Recovery Action Needed? on
page 6-4.
How Availability Works
The application takes the steps described in How Availability Works on page 6-5 during
recovery. The system takes additional steps to protect transactions and the integrity of
the Pathway/XM request queues.
For direct or replicated server classes, system recovery actions are those described in
How Availability Works on page 6-5. For distributed server classes:
•
Additional PATHMON processes are created automatically, as needed.
•
If the LCS process fails, the PATHMON process restarts it; a requester process
receives a communication error and must abort or restart its transaction. All
pending transactions sent to the LCS process are lost and must be retried; the
server class remains available because the PATHMON process has started a new
LCS process.