What’s The Point Of WLM?

(Originally posted 2014-11-09.)

At UK GSE Annual Conference I presented on DB2 and Workload Manager. It occurred to me that one of the slides was a good basis for a blog post, posing the question “what’s the point of WLM?” And this was the slide, with me “for scale purposes”. 🙂

(Thanks to Karen Wilkins for the photograph.)

So let me try to give you a synopsis of my view, expanding on each of the points on the slide.

Allows Scaling Like DFSMS

Back in 1988 I was one of the IBM Systems Engineers (SE’s) who supported a major UK customer in beta’ing DFSMS.[1] So I remember well the improvements in Storage Management that DFSMS brought.

Most notably the growth in data – data sets and volumes – was predicted to become unmanageable with the old ways of doing things. DFSMS, being Policy-Driven, provided constructs that enabled large numbers of volumes and data sets to be managed quickly.

The word “policy” is key to the analogy; WLM is also policy-driven, providing the same kind of leverage.[2] For many customers it would be inconceivable to manage performance with Compatibility Mode – even if it were still supported; The people cost would be too high, with the complexity of modern environments.

Much Simpler Than ICS / IPS / OPT

I’ll confess to never having been entirely comfortable with ICS / IPS / OPT; Sure I understood the mechanics but it was too early in my career to gather much experience of how it actually operated in real customer environments.[3]

There are, of course, people who “grew up” 🙂 with Compat Mode (and probably watched it evolve) and for them I’m sure it makes perfect sense.

For the pedants, yes we still have OPT (IEAOPTxx) but it is much simpler now.[4] And what was got rid of I think we can happily live without.[5]

Can Manage Newer Stuff

It’s been so long now since WLM became the only game in town that I forget the myriad enhancements that assume it’s present. So I’ll take one example area: Server Address Spaces.

There are at least three functions that use some variant of the Server Address Space mechanism:

  • WLM-Managed Initiators.
  • Websphere Application Server address spaces.
  • DB2 Stored Procedure server address spaces.[6]

All three of them rely on WLM to balance system conditions against goal attainment when deciding on whether to start additional address spaces. There was nothing like it in Compat Mode.

As I said, it’s one area and there are numerous others.

Can Manage Stuff “Properly”

I said WLM was policy-driven. From the outset the rhetoric was that you could couch the policy in business terms. For response time goals that’s obviously true. For velocity goals it’s little less clear.

Certainly WLM Importance can be used to separate, with clarity, important work from less important work.

So I think WLM enables you to much more closely align performance specifications with business goals.

Conclusion

This has been a brief synopsis. Much more and “TL;DR”[7] definitely would apply. And because it’s brief it’s had to be selective.

And if you think it egotistical of me to post a photo of myself, consider I look different from my previous avatar; Clearly older, but I probably don’t look wiser. 🙂

One final thought: There’s an enormous amount of Performance Tuning that has nothing to do with WLM; It’s important to be realistic about that; And anyone who talks about WLM like its some panacea – and people do – needs to be reminded of that.


  1. If I tell you I was an IBM SE you are supposed to understand my mindset and “get the hint”. The hint that I’ve been around a while and done interesting things. 🙂  ↩

  2. Both DFSMS (through ISMF) and WLM are panel-driven, wherein you manage the policy. I already take the WLM ISPF TLIB and generate reporting from it. I wonder if the same approach would work with ISMF.  ↩

  3. And the instrumentation – mainly in RMF but also in SMF 30 – is so much better, which really helps.  ↩

  4. And, again for the pedants, what’s been added to OPT is new, rather than reversing the simplification.  ↩

  5. Anyone care to challenge that?  ↩

  6. I wrote the Server Address Space Management chapters of DB2 for z/OS Stored Procedures: Through the CALL and Beyond in 2003.  ↩

  7. Too Long; Didn’t Read  ↩

Published by Martin Packer

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