IBM i > ADMINISTRATOR > SYSTEMS MANAGEMENT

How to Manage Prestart Jobs

Dawn May


Q: How can I better manage IBM i prestart jobs?

IBM i prestart jobs are used to handle client requests received from the network. Many types of prestart jobs exist, but the ones most commonly used are the host servers (ibm.co/2NMkI3z). Prestart jobs enable the jobs to be active, waiting for work, so that when a client request is received, the system can handle that request in a timely manner, typically eliminating the need to wait for a job to handle the work request.

Prestart jobs are good for overall performance—they move the expensive operations of starting and ending jobs out of the mainline performance path. Jobs are started ahead of time and wait for work requests that generally arrive from the network. Moreover, prestart jobs can be reused, which allows a single job to handle multiple requests. However, a trade-off exists between performance and management; managing prestart jobs is more complex than traditional batch or interactive jobs.

I often get questions about how to manage prestart jobs or how to understand the performance characteristics of workloads that use prestart jobs. Few easy answers exist because many variables and environmental aspects must be considered.

You need to ensure your prestart jobs are configured appropriately for your workload. For instance, you may want to route the work requests to different subsystems, or you may need to find a message logged to a job log in one of possibly hundreds of jobs, and will want to ensure you have strong security controls in place.

You’ll also want to understand the workload characteristics for prestart jobs, how to track that workload over time, how to monitor the basic performance information for prestart jobs, and how to understand which users are accessing prestart jobs, among other things.

Prestart jobs require many considerations, which I’ve covered in an extended series in my i Can blog (ibmsystemsmag.com/blogs/i-can). Topics include job entries, configuration settings, tuning, subsystem configuration, server type field and more.

Dawn May is a senior technical staff member at IBM in Rochester, Minn.


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