We just posted Episode 22 of Mainframe, Performance, Topics.
It features two of the longest topics we’ve ever recorded - and we think both of these topics warrant the time. If you want to fit this into your daily commute feel free to drive round the block a few times.
The Topics topic was particularly interesting in its gestation: It started out as a narrowish blog post of mine and then expanded into something much more general. While the iOS-specific bits might not be of especial interest to some of you, two things:
And we aimed that topic at both users and developers.
I would also highlight our new “Ask MPT” spot. We really do encourage questions. To quote David Brin “certainty is the lot of those who do not ask questions”. He makes certainty sound bad, doesn’t he?
And we had fun making this episode, so I guess we’ll do a few more…
Episode 22 “Great App-spectations”
Here are the show notes for Episode 22 “Great App-spectations”. The show is called this because we talk about app expections in our Topics topic.
We’ll use British spellings on these show notes, to be an equal opportunity documentation provider.
Where We’ve Been Lately
Marna has been to Istanbul, Turkey for the Tech U, February 6-8, 2019. Martin was nearly nowhere.
- z/OS V2.3 Enhancements RFA.
- z/OSMF Workflow is enhanced with the PTF for APAR PH03053 to support the array type of variable, which could contain a set of values. Good things will come from this.
"Ask MPT” New spot!
- Every podcast seems to have one: So we’ve decided to do a “Things people asked us” spot. Please submit questions!
- Q: How can you tell who used Dynamic Linklist (with LNKAUTH=LNKLST) to implicitly APF authorise a data set?
- A: In IEASYSxx (or on sysparm) LNKAUTH is specified or accept this as default. So when changing the linklist (and using this setting), you can see how APF authorisation is changing.
- Looking up SMF records, we see that SMF type 90 subtype 29 for Linklist change (SET). Just notice also that subtype 31 for LPA (SET or CSVDYLPA), 37 for APF (SET or CSVAPF).
Mainframe: PI99365 Two enhancements in z/OSMF Operator Consoles
- Support for “sticking” WTOR and held messages on the top of the console area
- Visible EMCS console name
Performance: Paging Subsystem Design in an age of Virtual Flash
Question from customer about need for paging space if Flash installed , which was answered in Martin’s blog post, but there is more thinking about this.
Look at the paging subsystem design in the round, with two flavours of Flash:
- Flash Express (in zEC12, z13) which is PCI-E cards
- Virtual Flash Memory (z14) carved from memory
- LPAR memory, but not the from that which a user defines for that LPAR
Design standpoint ideally as if no Flash
- Think about the economics vs risk of losing Flash. The reality is loss of Flash might cause ABENDs that matter. Damage assessment is worth thinking through.
- Flash is great - in the z/OS context - for handling dump capture, and spikes in memory demand in general.
Paging subsystem design: Two main considerations:
- Space: Ideally contain everything, particularly for dumping important address spaces
Come together in “30% Contiguous Slot Allocation Algorithm breakdown” rule of thumb
- Place local page data sets on separate volumes, even though virtualised.
- Fast disk, ideally SSD (Flash)
- 30% is not a hard and fast number, but we do see deterioation around the 30% mark.
Wrap up: Paging subsystem design still worthy of care, and establish whether risk of Flash or Virtual Flash warrants conservative configuration of paging subsystem.
Topics: Anatomy Of A Great App
“App” here means “third party software” but we’ll say app for short, because of the title of the episode. We are talking to app developers here.
- Marna is a low end user, and provides a different view. Doesn’t buy many apps, and doesn’t mind ads.
- Bad defaults are user hostile. Example is “geography default” is not where I am right now.
- Good provenance. Play Store is it.
- Signed apps that must pass multiple security app scanning.
- Sensible connections for cloud services (Google cloud and Google calendar)
- SMP/E installable might have been in the past, but z/OSMF-installable is the future standard.
- Uses documented interfaces.
- Instrumentation. Has appropriate SMF records.
- Security considerations. Critical.
- Sysplex enabled, when appropriate.
“Day One” support for hardware and software. Be hooked into your foundation.
- For z/OS TDMs / IBM Partnerworld
- For iOS WWDC
- Bug reporting being fit for purpose
- On iOS you have to have a Developer account, and it’s hard to get one.
- On z/OS we take bug reports from licensed customers
Decent documentation and samples.
Responsive developer social media presence at the usual sites. Social testing of apps is considerate.
Not a resource pig, with not umpteen copies of frameworks. Martin and Marna’s Facebook app was rather large, but maybe that is ok if that is a critical app. z/OS has had a problem with proliferation of WebSphere Liberty profiles.
Conclusion: Think about more than just what your app is supposed to do. Nobody wants software whose function they like but they hate using. It is way too easy to uninstall an app (or have hundreds of them and not use them).
Keep to the “Principle of least astonishment”.
Places we expect to be speaking at
- Marna will be at SHARE Phoenix March 11-15
- Martin will be March 12 GSE UK zCMPA Working Group - in London, with a new alpha presentation!
On the blog
Final signoff to a legend, John Dayka
- We have lost a dear friend, a trusted colleague, an incredible mind and an inspiring leader. John’s innovative contributions to Security over his prestigious career at IBM, his kindness to all peers, as well as his calm, level headed approach to all challenges will forever cement his legacy.
You can reach Marna on Twitter as mwalle and by email.
You can reach Martin on Twitter as martinpacker and by email.
Or you can leave a comment below. So it goes…