I recently answered a Facebook group thread about the frequency of doing an IPL. A couple of people said it’s a best practice to do one every week. One even said it was an “IBM best practice.” Of course, there’s no supporting documentation to support that claim. I’m sure it was an offhand remark by an IBM CE in 1997 while he or she was replacing a 4 GB disk drive. But a weekly IPL as a best practice? I completely disagree.
Performance. Database performance specifically.
The SQL Plan Cache is cleared during each IPL. It contains access plans for database accesses that were optimized by SQE. After an IPL, let’s say when a database query is run its access plan is rebuilt and then put into the Plan Cache for future use, making those eventual operations much faster. The IPL effectively takes those plans and throws them out the window, making database performance less efficient.
There’s no reason to IPL that often unless you have an abnormal problem, like a temporary storage issue. I’ve seen one particular software vendor recommend an IPL because their Java heap sizes fill up. Rather than fix the Java problem they instructed their customers to IPL once a month. Why? Well, the IPL will reset temp storage usage however the problem should be identified and properly resolved instead. How do you resolve those issues? Well, if it’s an IBM problem then it’s resolved by way of fix packs…in the IBM i world that means Program Temporary Fixes (PTFs). If you have a set PTF schedule then you’re already doing an IPL on a regular basis. Our managed services customers are mostly on a PTF refresh cycle every six months. A couple want to do them less often because they can’t get the downtime and some are more aggressive, wanting new PTFs every quarter for security purposes specifically. For the standard six month schedule (which I’d recommend especially if you don’t have any schedule at all), it means that we apply new PTFs temporarily then three months later we apply those PTFs permanently. Whether temporarily or permanently applying PTFs, all of our PTF updates require an IPL. Three months later we do another round of temporary PTFs. Rinse. Repeat. Since IBM has a cadence of releasing Technology Refreshes every six months, we find that it’s a great way to keep customers up to date and on a current Technology Refresh level.
Regular PTF updates will force an answer to another burning question: “how often should I do a full system save?” It depends. If you’re updating the Licensed Internal Code, IBM licensed programs and operating system (which you will most certainly do with a PTF update or OS upgrade), it’s definitely a good idea to do a full system save (GO SAVE option 21) or at the very least a SAVSYS (GO SAVE option 22) before and after.
So how often should you IPL? In my humble opinion your PTF and upgrade schedule should dictate your IPL schedule. Anything outside of that is an emergency. And the more current you are, the less emergencies you should have.