Chapter 11. Sysplex terminal management (STM) operations 247
If no response soon, user has choice.
Keep trying until response arrives (may have to wait for IMS1 to restart).
/EXIT conversation and do other work. Even though conversation is exited, it will still be
scheduled and processed. When the output is queued and retrieved by an interested
IMS, the conversational abnormal termination exit (DFSCONE0) will be driven to
handle it.
11.6 Recovering Fast Path
When SRM=GLOBAL and RCVYFP=YES, Fast Path response mode can be recovered on
any IMS in the IMSplex. This means that, if a user is in Fast Path response mode when IMS
fails, that user can log on to any IMS in the IMsplex. When logon and signon is complete, the
user session will be put into response mode. When the output message becomes available, it
will be delivered to the user.
A detailed example of how this is done is not shown here, but it is similar to recovering a
conversation. There is a Fast Path input message in progress (FP-IP) flag that performs the
same function that the CONV-IP flag performed.
There is one significant difference, however. When SRM=GLOBAL but the transaction is
processed locally without going through the EMHQ (sysplex processing code = local-only or
local-first), then its SRM is
temporarily changed to LOCAL. When this occurs, if IMS fails,
ownership of the resource will not be released and the user must wait for the failed IMS to
restart.
Note also that, when RCVYFP=NO, all Fast Path output messages are deleted if IMS or a
session fails. They are not recoverable and will be deleted when discovered on the shared
queue.
11.7 Recovering STSN sequence numbers
Recovery of STSN sequence numbers is much simpler than recovery of conversations or
Fast Path. The input and output STSN sequence numbers are maintained in the (static node)
USER entry and, when logging on to another IMS, can be used to resynchronize the
message traffic with the STSN device. The intent of STSN is to resolve the
in-doubt message.
For example, if IMS sent a message to a terminal but did not get an acknowledgment, IMS
does not know whether the message was received or not. By informing the STSN device of
the sequence number of the last output message, the device can ask IMS to resend it, or it
can tell IMS to dequeue it. A similar function applies to an input message when the STSN
device does not know if it was received by IMS.
By supporting STSN recovery, the user can log on to another IMS. Using the sequence
numbers in the resource entry, that IMS can resynchronize its input and output messages
with the STSN device.
11.8 Summary of STM in action
The above descriptions and examples, although quite detailed, are meant to give the reader
some idea of how sysplex terminal management works, and the impact that various actions
and failures can have. It is not complete.

Get IMS in the Parallel Sysplex Volume III IMSplex Implementation and Operations now with the O’Reilly learning platform.

O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.