Addressing OLTP Solutions with CICS: The Transaction Server ... - Ibm

10.7.1.1 Pseudo Conversational and Conversational Transactions
Pseudo conversational programming is based on the fact that, in a
conversational transaction, the length of time spent in processing each of a
user′s responses is extremely short when compared to the amount of time
waiting for the input. A conversational transaction is one that involves more
than one input from the terminal, so that the transaction and the user enter into
a kind of conversation. A nonconversational transaction has only one input (the
one that causes the transaction to be invoked). It processes that input, responds
to the terminal, and terminates.
In a conversational transaction, processor utilization times, even allowing for
accessing files, are considerably shorter than terminal transmission times, which
are considerably shorter than user response times. This is especially true if
users have to think about the entry or enter many characters of input.
Consequently, conversational transactions utilize storage and other resources
for much longer than nonconversational transactions.
A pseudo conversational transaction sequence contains a series of
nonconversational transactions that look to the user like a single conversational
transaction involving several screens of input. Each transaction in the sequence
handles one input, sends back the response, and terminates.
Before a pseudo conversational transaction terminates, it can pass data forward
to be used by the next transaction initiated from the same terminal, whenever
that transaction arrives. A pseudo conversational transaction can specify what
the next transaction is to be, and it does this by setting the tranid of the
transaction which is to handle the next input. However, be aware that if another
transaction is started for that device, it may interrupt the pseudo conversational
chain you have designed.
No transaction exists for the terminal from the time a response is written until
the user sends the next input and CICS starts the next transaction to respond to
it. Information that would normally be stored in the program between inputs is
passed from one transaction in the sequence to the next using the COMMAREA
or one of the other facilities that CICS provides for this purpose.
10.7.1.2 Correspondence of CICS Client Processes and Servers
In a typical CICS system there is likely to be a small pool of application servers
servicing requests from a much larger pool of CICS cicsterm and cicsteld
processes.
It is important to understand that a conversational transaction requires exclusive
use of an application server, thereby reducing the total number of servers
available to process other requests. CICS will create additional servers as
dictated by system demand up to a maximum number that you can configure, but
once you reach this limit no more will be created. Therefore if you design all of
your applications to be conversational, there is a considerable risk that CICS will
be unable to service user requests to run transactions.
Chapter 10. Application Design Considerations 151