When Display Commands Aren’t Good Enough

(Originally posted 2011-03-13.)

There’ve been times in the past when a request for extra data in SMF has been met by "you can issue a DISPLAY command to get that". (Another variant is "you can go to the HMC for that".)

I’m here to tell you why I don’t think that’s a brilliant answer:

  • Such a command is a point-in-time thing.

    Systems nowadays are much more dynamic than they were. Something as simple as the number of engines assigned to an LPAR is highly likely to change – from one moment to the next.

    So you really can’t tell what happened last week from the results of a command you issued just now.

    And automating the command on a timer pop is a touch fraught as well.

  • The output from commands is usually much harder to parse than well-designed written-out records.

    (That’s true whether we’re talking about SMF or some other kind of instrumentation .)

  • The Systems Management environment is worse, too.

    I’m not sure I really want to permit Performance people to issue operator commands, just so they can get instrumentation. Look, we’re all splendid lads and lasses (I’m quite sure) but I really don’t think it’s good for Systems Security to let us do it: To make it even acceptable we have to put bounds around what commands and parameters are permitted.

    (Think of "F LLA" as a good example of where the same command can be used to change things and get some answers.)

    And as for going to the HMC… 🙂

  • An interesting case is the DB2 Catalog: While it generally has static information in it there is some time-driven stuff (such as in SYSCOPY and the "HIST" tables).

I think we’re very lucky in z/OS to have good instrumentation in the form of SMF (and possibly things like DB2 logs). It’s the sort of thing many other platforms should be envious of. And, yes, I do value the ability to get "here and now" information (not least for driving Automation).

One other thing: If the information is available for an operator command it’s just a SMOP (Simple Matter Of Programming) to get it into SMF. (Yes, I know it’s not quite that simple: Having rubbed shoulders with developers for 25 years I do appreciate that.)

So you’ll see why I keep pushing for stuff to go into SMF. And I hope you’ll keep pushing, too. 🙂

Published by Martin Packer

I'm a mainframe performance guy and have been for the past 35 years. But I play with lots of other technologies as well.

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