Terminal control: design for performance

This list shows you what you need to consider for terminal control when designing for performance.

• Minimize the length of the data stream sent to the terminal.

  Good screen design and effective use of 3270 hardware features can significantly affect the number of bytes transmitted on a teleprocessing link. It is important to keep the number of bytes as small as possible because, in most cases, this is the slowest part of the path a transaction takes. The efficiency of the data stream therefore affects both response time and line usage.

• Use only one physical SEND command per screen.

  It is typically more efficient to create a screen with a single call to BMS, than to build the screen with a series of SEND MAP ACCUM commands. It is important to send the screen in a single physical output to the terminal. It is very inefficient to build a screen in parts and send each part with a separate command, because of the additional processor overhead of using several commands and the additional line and access method overhead.

• Use the CONVERSE command.

  Use the CONVERSE command rather than the SEND and RECEIVE commands (or a SEND, WAIT, RECEIVE command sequence if your program is conversational). They are functionally equivalent, but the CONVERSE command crosses the CICS services interface only once, which saves processor time.

• Limit the use of message integrity options.

  Like specifying the WAIT option on the final SEND command of a transaction, the MSGINTEG option of CEDA requires CICS to keep the transaction running until the last message has been delivered successfully. The PROTECT option of the PROFILE definition implies message integrity and causes the system to log all input and output messages, which adds to I/O and processor overhead.

• Avoid using the DEFRESP option on SEND commands.

  Avoid using the DEFRESP option on SEND commands, unless the transaction must verify successful delivery of the output message. It delays termination of the transaction in the same way as MSGINTEG.

• Avoid using unnecessary transactions.

  Avoid situations that can cause users to enter an incorrect transaction or to use the CLEAR key unnecessarily, thus adding to terminal input, task control processing, terminal output, and overhead. Good screen design and standardized PF and PA key assignments should minimize this.

• Send unformatted data without maps.

  If your output to a terminal is entirely or even mostly unformatted, you can send it using terminal control commands rather than BMS commands (that is, using a BMS SEND command without the MAP or TEXT options).