Fix to the way extents are calculated in SYSTABLEPART

(Originally posted 2006-01-12.)

Running out of extents for DB2 tablespaces can be a real bore. So installations like to monitor them (and I like to see them too). APAR PK12653 describes a fix to the recording of the number of extents in the SYSTABLEPART Catalog table. This fix is only available for DB2 Version 8.





RUNSTATS updates this table using the extents count in the PB0 control block. This is updated on physical data set OPEN, but not when the data set gets extended. So it can be inaccurate.





The changes are two-fold:

  • Refresh the PB0 value at the end of extend processing.
  • Notify other data sharing members at the end of extend processing.

This should make the number a lot more accurate in SYSTABLEPART because RUNSTATS will be sampling a more accurately maintained control block field.

Better Routing of DDF Work in a Parallel Sysplex with z/OS 1.7

(Originally posted 2006-01-12.)

I’m working through the queue of interesting APARs that have been sitting in my in-basket. (I guess it’s a “New Year’s tidying up” thing.) 🙂 Here’s one that relates to workload routing for DDF. It does prereq z/OS R.7 on all members so it won’t be of that much interest to customers right now…

APAR PK03045 “DB2 z/OS support for z/OS 1.7 WLM routing service” describes the DB2 enhancement to support this new routing algorithm. This is available for both DB2 Version 7 and Version 8.

In a nutshell the “old” WLM algorithm used to provide routing recommendations to interested clients based on available CPU capacity. However that didn’t take into account anything else that within DB2 that might cause a particular Data Sharing Group Member to be a poor placement choice. DB2 has been changed to ensure that WLM has accurate information about the delay, or queue, time of any of the enclaves that DB2 DDF created and used to perform its work requests. Recall: in-bound DDF work acquires an enclave when it goes through the initialisation process in the DIST address space, prior to executing SQL.

This enhancement advances the state of the art when it comes to workload balancing – a topic that has recently exercised my brain more than it had in the past. I would be interested in hearing of customers’ experiences in this area, whether DB2 or not.

DB2 Catalog and Performance Trace Mismatch

(Originally posted 2005-12-01.)

If you ask Performance Trace nicely enough it’ll tell you what statement in a package is consuming all the CPU.

Over the past couple of years we’ve been working on code to analyse the DB2 Catalog and PLAN_TABLE tables to do SQL tuning. It’s been an interesting journey – and, I guess, a never-ending one.

Each client provides fresh insight and challenges. Our current Chinese one is just such a client: The statement numbers in Performance Trace and SYSIBM.SYSPACKSTMT/PLAN_TABLE don’t always tie up. SYSPACKSTMT and PLAN_TABLE agree with each other. It’s the Performance Trace that’s anomalous.

It turns out that the static data and the Performance Trace were collected some weeks apart. In a busy installation code gets edited, tested, recompiled all the time. Particularly if the code is underperforming. I think we got bitten by that.

So in the future we’ll be surer to try and get fresh Catalog/PLAN_TABLE data when we take a trace – which probably means a respin as we generally home in on a particular package to trace after the main DB2 (and z/OS) study is done. Unfortunate but necessary.

DB2 in 64 Bit Mode and Hiperpools

(Originally posted 2005-11-23.)

A recent client of mine is still using Hiperpools – while in 64-bit mode (and with > 2GB of memory on each LPAR).

It is my contention that they would save CPU, and probably get better buffer pool effectiveness, if they switched to a judicious mixture of virtual pools and data space pools.

Would any reader care to relate their site’s experience with this sort of reconfiguration?

In this post by virtual pools I mean those backed by DBM1 virtual storage, rather than data space or hiperpools. So virtual pools contribute towards the tally of DBM1 virtual storage usage, which (as we all know) is limited to significantly less than 2GB.

This client is on Version 7 – and I expect them to remain there for a while. I do know – from IFCID 225 (Statistics Trace Class 6) – that they can’t replace the whole of their current hiperpool inventory with virtual pools. So some mixture of data space and virtual is inevitable.

Inside Big Blue – Great Web Stuff

(Originally posted 2005-11-20.)

IBM Shows del.icio.us… is a very interesting article by David Weinberger (author of The Cluetrain Manifesto) about all the interesting things going on on the web.

I’m proud to say that IBM is doing a lot of these interesting things – and I’ve taken time over the last two years to become a part of them. David spent a day at a seminar where all of these interesting things were demo’ed. I’d encourage you to read his blog entry and see how some of those things could apply to your organisation. And I’m sure you’ll think some of them off the wall but we are genuinely finding most of them useful. And I personally can attest to that.

Take blogging for instance. As Apple found out (with their Nano) it’s important to know what the blogosphere is saying about you. And it’s far more than just Googling your own name. 🙂

Queen: Return of the Champions DVD

(Originally posted 2005-11-14.)

As many people know I’ve been a Queen fan since 1974. And us Queen fans all know how we feel about Freddie Mercury’s death and the subsequent retirement of John Deacon. So it was with a mixture of anticipation and trepidation that I saw Queen + Paul Rodgers live in Hyde Park this summer. That was a great show. As these guys are all about 15 years older than me it’s nice to see that in a notoriously youth-oriented business they could still deliver. The parallel with the IT industry is obvious (not that I have to mention it to be able to blog here).:-)

So on my way through Heathrow I picked up the Queen: Return of the Champions DVD. It was all shot at a concert in Sheffield (with the exception of a very nicely done Imagine which was from Hyde Park).

I have to tell you it recreated the buzz I got when QPR strode onto the stage at Hyde Park. But this time I could see much more.

So, for Queen fans who can cope with the idea of Brian and Roger touring with someone other than Freddie, or for Paul Rodgers fans, this is one nice DVD.

A Movie You Might Like

(Originally posted 2005-11-14.)

At the weekend I went to see Flightplan, starring Jodie Foster and Sean Bean.

I thoroughly enjoyed it, despite the suspense of disbelief element. But it is a bit far-fetched.

To describe the plot – any further than the marketing material does – would be to totally spoil it for anyone who is thinking of seeing the movie. All I can say is that it is an airplane thriller, in the mould of Airforce One, which I also enjoyed.

But as someone who flies a lot I have to remind myself: This is a work of fiction.

Hardware Model Support in z/OS Release 7 RMF

(Originally posted 2005-11-11.)

This probably counts as my contribution to RMF for this decade. 🙂

RMF has long had the Software Model for a processor in SMF 70. Until z900 this was the same as the Hardware Model. With z900 you could have processors that were there but you hadn’t bought yet.

With z990 it got a lot worse as you could have between 1 and 4 books on the processor.

In z990 (and z9-109) studies we would know, for example, that the processor was a z990 Model 324 but wouldn’t be absolutely sure whether it was a 3-book or a 4-book machine. With a 324 there’s nowhere to go without installing a fourth book – if you needed to add processors. And we, frustratingly wouldn’t know that.

Now, with Release 7 RMF we get the hardware model in addition to the software model. So we expect in future engagements to be a little more sensitive to what it would take to upgrade.

Actually here’s what you could do today – on Release 6 or prior…

The Logical Processor Sections in the SMF 70 record do record under the PHYSICAL LPAR the processor numbers. Here’s what I saw for the above-mentioned z990 Model 324:

  • 00,02,05,07,08,0A,0C,0E
  • 20,22,25,27,28,2A,2C,2E
  • 30,32,35,37,38,3A,3C,3E

I wrote those in 2-digit hex format for a reason: The first digit is the book number.

So where’s Book 1, then?

It doesn’t exist. So I conclude this is a C24 (3-book) machine.

If this was your machine you’d probably be saying Well, I know I bought a 3-book machine but, in my consultancy, I think I’d like to know that, too.

One other thing: You can tell what the engine type is from these sections. In this case they’re all General-Purpose CPs (GCPs) and that corresponds to what we happen to know about the client: 2 12-way dedicated LPARs and no ICFs, IFLs or zAAPs.

Now none of that is an “intended interface” but it is fascinating. 🙂 But you are much better off with the 1.7 support for Hardware Model.

DDF and EWLM

(Originally posted 2005-11-11.)

I’ve not really gotten into EWLM and ARM – yet. But I think this APAR will be of interest to those who have. And I expect I will get interested in it when it’s more fully established…

PK11801 DDF FULLY-ENABLED EWLM ARM SUPPORT describes how the DDF support for EWLM / ARM is being made available to the general population of DB2 Version 8 sites. To quote:

DB2 for z/OS’ support for EWLM was initially shipped via APAR PQ91509. The support was installed disabled to control its initial use by customers while studies, etc., were performed to assess the support’s impact on a customer’s system and to evaluate if any further enhancements would be required. That investigation has concluded and additional enhancements have been provided on z/OS to minimize the impact of EWLM monitoring on a z/OS system. With the initial use period being concluded, the support will no longer need a special user modification to activate it.