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LongEx Mainframe Quarterly - November 2024

Throughout my career, I've believed that IBM has the best mainframe documentation and supporting resources of any vendor or platform.

Their manuals are great, their Redbooks brilliant, and they'll fix things that are broken: fast. In particular, their support site is sensational. But you may be surprised how much you can find in this treasure chest.

Self Help To Fix Problems

Although IBM documentation is brilliant, it is not comprehensive. Let's take an example. Suppose our CICS region is going to maxtasks, and we don't know why.

IBM support document 338143 describes a problem when a CICS region goes to maxtasks. It explains that setting the SIT MROFSE parameter to YES in an Application Owning Region (AOR) can result in CSMI transactions not ending, risking a maxtask situation. Finding this document may save us opening a PMR and help us fix our problem quickly.

This is one of several documents describing CICS maxtask related issues. As with all sites, there are tricks when entering search arguments. IBM provide an IBM support document with some hints.

Best Practices and Recommendations

IBM support pages don't just provide self-help to fix problems. They also provide IBM's recommendations and best practices that may not have made it into their documentation.

For example, document 670323 provides recommendations on isolating VSAM record level sharing workloads into separate coupling facility structures. Document 7150566 provides some performance best practices for z/OS Connect. Document 6354681 provides some best practices when taking and managing z/OS standalone dumps.

Handy Information and Answers

IBM support pages also include handy information, or answers that you can't find elsewhere. For example, document 724549 provides a replay of a webcast relating to CICS and DFSMStvs. Document 707661 answers the question "Are there any advantages to using VSAM record level sharing (RLS) with CICS Transaction Server for z/OS (CICS TS)?" Finally, document 6354485 provides an IBM presentation showing how to implement z/OS dataset encryption.

How Products Work

IBM APARs often have information about how their software works that expands on their documentation and can be brilliant. For example, support document 6144987 explains how to set a z/OS SLIP trap to create an SVC dump when a CICS region goes to maxtasks. This is a great way of diagnosing why a CICS region has reached maxtasks.

But you can get more information from this document. It talks about a control block called the Common System Area (CSA), with a link to more information in CICS documentation. It further highlights that there is a bit in the CSA (CSAMXTON) that is set when CICS reaches maxtasks.

From this information, we know that the CSA is a control block used by CICS. Looking at the CICS documentation shows that this control block holds a lot of other information.

APAR II04843 also mentions the CSA and shows how it stores the SVC numbers used by CICS. APAR PK73703 explains that another control block called the AFCB holds the address of the CSA.

From here, we can search documentation and other resources to find out more about the CSA. For example, the CICS documentation shows how it is formatted by the CICS IPCS VERBEXIT, and explains that the CSA has an option extension: the optional features list.

New Features

IBM will sometimes introduce new features via APARs. The IBM support site documents these APARs, describing the new features and documentation changes required. For example, APAR OA61271 adds the 'Bypass Extent Check' feature for BSAM access to sequential datasets and provides documentation updates for this new feature. APAR PH23753 adds a new utility added to the IMS High Performance Sysgen Tool.

The IBM support site even has a page that can be used to list and search APARs introducing new features or functions.

IBM Documentation

Suppose we want to find out more about VSAM RLS performance for our CICS programs. Which documentation should we look at: z/OS or CICS? Maybe other products could impact this as well?

Try searching in the IBM support site using the search string "VSAM RLS Performance." This will show relevant APARs and some presentations, but also links in z/OS, CICS, DFSMSdss, and even Rational ClearCase documentation. It also has links to product announcements and more. Could be handy if we're looking for things outside of CICS that are affecting our performance.

A Key Part of Your Toolbox

The IBM support site is simply, brilliant: a key part of any mainframer's toolbox.

David Stephens