IMS Address Space Taxonomy

(I’m grateful to Dougie Lawson for correcting a few errors in the original version of this.)

I don’t often write about IMS and there’s a good reason for it: Only a small proportion of the customers I deal with use it. I regard IMS as being one of those products where the customers that have it are fanatical – in a good way. 🙂

So when I do get data from such a customer I consider it a golden opportunity to enhance my tooling. And so it has been recently. I have a customer that is a merger of three mainframe estates – and I have data from two of the three heritages. Both of these have IMS.

This mergers happened long ago but, as so often happens, the distinct heritages are evident. In particular, the way they set up the IMS systems and regions differs.

You can, to a first approximation, separate IMS-related address spaces into two categories:

  • IMS System Address Spaces
  • IMS Application Regions

In what follows I’ll talk about both, referencing what you can do with SMF 30, specifically. Why SMF 30? Because processing SMF 30 is a scalable method for classifying address spaces, as I’ve written about many times before.

IMS System Address Spaces

IMS system address spaces run with program name “DFSMVRC0” and there are several different address spaces. For example, over 30 years ago the “DL/I SAS” address space became an option – to provide virtual storage constraint relief. It;s been mandatory for a long time. Also there is a DBRC address space. All have the same program name.

The system address spaces have Usage Data Sections which say “IMS”. The Product Version gives the IMS version. In this customer’s case one part of the estate says “V15” and the other part “V14”.

The IMS Control Region is the only system address space that can attach to Db2 or MQ. So, if the program name is “DFSMVRC0” and there are Usage Data Sections for either Db2 or MQ we know this is the Control Region. But this isn’t always going to be the case – as some IMS environments connect to neither Db2 nor MQ. So here the Product Qualifier field can be helpful:

  • Both DBRC and Control Region address spaces have a Product Qualifier of “TM”. But you can’t necessarily tell them apart from things like I/O rates. However, you might expect a DBRC address space to have a name with something like “DBR” in. (I’m not wowed by that level of fuzziness.)
  • A DL/I SAS has Product Qualifier “DBCTL”.

I’m going to treat IRLM as an IMS System Address Space, when really it isn’t. This is the lock manager – and it’s the same code whether you’re running IMS or Db2. The program name is DXRRLM00 and there is little to distinguish between an IRLM for IMS or for a Db2 subsystem in SMF. (In fact which Db2 an IRLM address space is associated with isn’t in SMF either.) the best my code can do is parse job names, service class, report class etc names for “IMS” or, still worse, “I” but no “D”.

IMS Application Regions

IMS application address spaces – whether MPRs or BMPs – run with program name “DFSRRC00”. They also have Usage Data Sections that say “IMS” but don’t – in the Product Qualifier field – say anything about the subsystem it’s using. Similarly, when CICS attaches to IMS it’s Product Qualifier isn’t helpful.

To my mind the distinction between a MPR (Message Processing Region) and a BMP (Batch Message Processor) is subtle. For example I’ve seen BMPs that sit there all day, fed work by MQ. You probably would glean something from Service Classes and Report Classes. Relying on the address space name is particularly fraught.

Two Diverse IMS Estates

This latest customer has two contrasting styles of IMS environment, mainly in their testing environments:

  • One has lots of very small IMS environments.
  • the other has few, larger testing environments.

Also, as I noted above, one estate is IMS V14 and the other is V15. This does not appear to be a case of V15 in Test/Development and V14 in Production.

So I guess their testing and deployment practices differ – else this would’ve been homogenised.

I’m going to enjoy talking to the customer about how these two different configurations came to be.

Conclusion

IMS taxonomy can be done – but it’s much messier than Db2 and MQ. It relies a lot on naming conventions and spotting numerical dynamics in the data.

Note: For brevity, I haven’t talked about IMS Datasharing. That would require me to talk at length of XCF SMF 74–2 and Coupling Facility 74–4. Something else I haven’t discussed is “Batch DL/I” – where a batch job is it’s own IMS environment. This is rather less common and I haven’t seen one of these in ages.

I would also say, not touched on here, that SMF 42–6 would yield more clues – as it documents data sets.

And, of course serious IMS work requires its own product-specific instrumentation. Plus, as Dougie pointed out to me, the Procedure JCL.

Published by Martin Packer

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