Too Extensive API Call
Volvo Information Technology in Gothenburg, Sweden, received complaints about long response times for a certain frequently used menu option. iPerformance was asked to assist with finding the cause, which appeared to be a too general call to an API.
Many APIs can return a very wide range of information about e.g. files. When using CL commands to retrieve data about objects, the command processor programs often ask the API for all data available, which in most cases is much more than needed, causing use of much more resources on I/Os to collect the requested data from the different system objects contain within a file. That was indeed what happened in this case.
By changing the code to call the API directly and only ask for the needed minimum of data, the response time changed to subsecond from an average of around 10 seconds.