z/OS Upgrades Impact on DFSORT

Why z/OS and DFSORT Are Linked

DFSORT is an IBM product that is supplied with or for z/OS. The level of DFSORT that is installed is typically tied to the z/OS release (or the release plus service). When the operating system is upgraded, the systems programmer or software management process often updates DFSORT to the level that is supported or recommended for that z/OS level. So from an application perspective, a z/OS upgrade is a common time when DFSORT "changes" even if you did not request a separate DFSORT upgrade.

What Can Change

A newer DFSORT version can introduce new control statement options and features. It can also deprecate (mark for future removal) or remove old options. Default values for some options may change so that jobs that did not explicitly code the option behave differently. Bug fixes in DFSORT (delivered via PTFs or in the new base) can change output in edge cases—for example, a fix for overflow handling might change the value written in a SUM field when overflow occurs. So after a z/OS (and thus DFSORT) upgrade, jobs that used deprecated or removed syntax may fail; jobs that relied on old defaults or on buggy behavior may produce different results.

Before the Upgrade

Identify the DFSORT (or sort product) level that will be in effect after the z/OS upgrade. Use the product documentation or your site's upgrade plan. Read the release notes and migration material for that level. List deprecated and removed options and any noted default or behavior changes. Then inventory your batch jobs: which ones use those options or rely on that behavior? Plan the control statement updates. If you have a test system that will be at the new level before production, run the affected jobs there and compare output to a baseline from the current level.

PTFs and Fixes

PTFs (Program Temporary Fixes) are maintenance updates. When z/OS is upgraded or when PTFs are applied, DFSORT can receive fixes. A fix might correct a defect that caused incorrect output in rare cases—so after the fix, output might change. A fix might also "tighten" validation and reject control cards that were previously accepted. PTF descriptions usually indicate the component (e.g. DFSORT or the sort product name). When planning or troubleshooting after an upgrade, consider whether recent PTFs could affect the sort step.

After the Upgrade

Run your critical DFSORT jobs and check for abends or new messages. If a job fails, look up the message in the manual for the new DFSORT level. Update control statements as needed (e.g. replace deprecated options). Compare output (record count, key records, totals) to pre-upgrade results for a sample of jobs. Document any jobs that required changes so that future upgrades and maintainers have a reference.

Finding the Right Documentation

Use the DFSORT (or sort product) documentation that matches the level installed with your z/OS release. IBM publishes documentation for each product level; the exact title and location depend on how your site accesses IBM docs (e.g. IBM Knowledge Center, PDF). The first messages in a sort step SYSOUT often include the product name and version—use that to confirm which level is running and which manual to use.

Explain It Like I'm Five

When the big computer (z/OS) gets an update, the sorting tool (DFSORT) that comes with it might get an update too. Some old buttons might be gone or work differently. Before the update, the grown-ups read the new instructions (release notes) and fix the jobs that use those buttons. After the update, they try the jobs to make sure everything still works.

Exercises

1. Why might your DFSORT job fail or behave differently after a z/OS upgrade even though you did not change the job?
2. Where would you find which DFSORT version is active after the upgrade?
3. What are two things you should do before the upgrade regarding sort jobs?
4. How can a PTF that "fixes" DFSORT change job behavior?