Improving performance of intersystem START requests
In many inquiry-only applications, sophisticated error-checking and recovery procedures are not justified. Where the transactions make inquiries only, the terminal operator can retry an operation if no reply is received within a specific time. In such a situation, the number of messages to and from the remote system can be substantially reduced by using the NOCHECK option of the START command.
About this task
Where the connection between the two systems is via the z/OS Communications Server, this can result in considerably improved performance. The price paid for better performance is the inability of CICS to detect some types of error in the START command.
A typical use for the START NOCHECK command is in the remote inquiry application described at the beginning of this section.
The transaction attached as a result of the terminal operator's inquiry issues an appropriate START command with the NOCHECK option, which causes a single message to be sent to the appropriate remote system to start, asynchronously, a transaction that makes the inquiry. The command should specify the operator's terminal identifier. The transaction attached to the operator's terminal can now terminate, leaving the terminal available for either receiving the answer or initiating another request.
The remote system performs the requested inquiry on its local database, then issues a start request for the originating system. This command passes back the requested data, together with the operator's terminal identifier. Again, only one message passes between the two systems. The transaction that is then started in the originating system must format the data and display it at the operator's terminal.
If a system or session fails, the terminal operator must reenter the inquiry, and be prepared to receive duplicate replies. To aid the operator, either a correlation field must be shipped with each request, or all replies must be self-describing.
An example of intercommunication using the NOCHECK option is given in Figure 2.
The NOCHECK option is always required when shipping of the START command is queued pending the establishment of links with the remote system (see Local queuing of START commands), or if the request is being shipped to IMS.