Availability Guide for Application Design

Availability in the Pathway Transaction-Processing
Environment
Availability Guide for Application Design—525637-004
6-19
How Does the Pathsend Facility Work?
Pathsend requesters are typically used where the number of transactions is high but
the number of devices is low. For example, Pathsend requesters often provide
message control for client processes running on systems other than HP systems. The
TDP explained under Availability Through RSC/MP on page 6-11 is one example of
such a Pathsend requester. Figure 6-5 on page 6-19 shows a Pathsend requester
acting on behalf of a client process on an IBM mainframe connected to the HP system
using a SNAX line.
Another likely use of a Pathsend requester might be for low-priority batch-type
transactions from a single source such as a tape. Refer to Section 4, Data Protection
and Recovery, for a discussion on mixing online operations and batch operations.
Applications that use many devices with a low number of transactions from each
device should not use a Pathsend requester for each device because of the high
overhead associated with running many extra processes. Suitable alternatives include:
•
Writing your own multithreaded Pathsend requester. Refer to the NonStop TS/MP
Pathsend and Server Programming Manual.
•
Using the Pathway terminal control process (TCP) as described under Availability
Through Pathway/iTS on page 6-24.
The following sequence shows the skeletal outline of a typical Pathsend application
when operating normally. Familiarity with this sequence will be helpful in understanding
the recovery requirements and procedures described later in this subsection.
1. The Pathsend requester begins a transaction and gets a transaction identifier. If
the requester is a process pair, it typically checkpoints all relevant state information
to its backup process at this point.
Figure 6-5. Components in a Typical Pathsend Application
Server
Server Class
Pathsend
Requester
LINKMON
PATHMON
Database
NonStop TS/MP
IBM Host
SNAX
Client
VST505.vdd