2022-04 A brief history of the Universal Tablespace (UTS) Part Two

This month I wish to finish off, what I started last month, my musings about UTS over the releases and years.

Db2 12 Changes to the UTS Picture

For Partitioned By Range (PBR), a brand-new space was created called the UTS PBR Relative Page Number (RPN) which was, in my opinion, the best thing in Db2 12! Quite simply, it allows the dynamic ALTERing of the partition and all of the related partitioned indexes DSSIZE on-the-fly even when a LOAD is running! This was great! Any users out there who have had a nightmare LOAD? Yep, now, as long as you are actively monitoring your data and index partition sizes, you can issue these ALTERs automatically and never hit the buffers like you do today.

DSSIZE gets propagated through

To enable this feature DSSIZE was improved to be settable at the data partition level and also extended to partitioned indexes. The available values were changed to allow any integer from 1 GB to 1024 GB. This allows extreme flexibility for all sizing requirements. Note, however, that NPSIs are still stuck in the middle of nowhere with just PIECESIZE as a helping hand…

Everything groovy???

So, what was wrong with this picture? Well, the change from PBR to PBR RPN was, shall we say, a little bit painful. The RID size got extended and as the RID is stored in *every* header page it required a tablespace reorg with partition-based inline image copies. Now, as you can well imagine, most people’s PBRs are pretty big, and allocating 4096 Virtual Tapes in parallel was just not going to happen! After a while IBM enhanced REORG so that you could put multiple copies on one tape, sort of like STACK, but much better – and not just for Tape but also for DASD. This has really accelerated the acceptance and usage of PBR RPN.

The future is bright!

Check this Blog entry:


It is revealed that in Apollo (Db2 for z/OS vNext – Which has now been released as Db2 13 for z/OS), the ability to migrate from a PBG to a PBR will become available instead of the UNLOAD, DROP, CREATE, LOAD method which is the only way up until Db2 12. This will be very handy as the PBR RPN is the best way to go forward with large tablespaces (>60 GB) as long as you have *some* sort of available partitioning scheme, of course!

No more worries??

What do you need to worry about now? Well, you remember that huge LOAD I mentioned earlier that comes at the partition level? You must simply monitor the sizes of your partitioned objects and add a few GBs of space when required, on the fly, with no outage.


Well, we have a little product called SAX+ which does exactly that! It starts the required OPx IFCID traces and computes the values against given thresholds, then automatically issues the ALTERs giving you a seamless experience with PBR RPNs. The only “problem” left now is when you are approaching the 1024 GB absolute PBR RPN physical limit. SAX+ warns you about this as well. Then you will have to either schedule a REBALANCE or a new LIMITKEY definition and REORG to spread the load again. However, when you know this well in advance it is no longer a serious problem!

Not yet at PBR RPN? – No problem!

PBRs which are not yet RPNs are monitored to warn when a threshold of usage in a data or index partition is exceeded. This also gives you more than enough lead time to get the REORG ready to switch it to RPN or just resize/rebalance your partitions.

What about PBGs?

PBGs are also fully supported within SAX+ as it can automatically add partitions, if desired, which additionally avoids SQLCODE -904’s. Plus, SAX+ adjusts the way it works depending on the MAXPARTITIONS and the actual number of allocated partitions. For example, MAXPARTITIONS 10 with a 90% warning would alert you when the ninth partition is allocated and in use. When the tenth partition gets allocated the warning switches from an LDS warning (Running out of available partitions) to a “last partition” filling up warning similar to PBRs which are not yet RPNs. This obviously helps a lot when you have MAXPARTITIONS 1 which is the IBM recommendation these days.

Anything else?

Naturally, SAX+ also takes care of the other problems that can catch you unawares:

  • Running out of Linear Datasets (LOB, PBG, XML, non-UTS space and NPSI)
  • Running out of space
  • Running out of extents and also badly fragmented extents
  • Running out of volumes
  • Running out of physical range for SEQUENCES or IDENTITY columns
  • Running out of physical range for Numeric Primary key columns
  • Running out of DBATs
  • Running out of space in SMS Storage Groups

All of the entries in the above list are very annoying when they hit you with no warning, especially running out of Linear Datasets. Think NPSIs here! Every PIECESIZE is an LDS and so you can run out of these quicker than you think.

LOG problems?

One last thing that SAX+ can help you with is detecting Db2 Log problems together with stalled logs… Not something you normally think of with a space management tool! When Db2 starts running out of space in active logs it issues the DSNJ110E message and I know shops who have „missed“ this alert. The problem was that the Db2 Log SMS Storage Group was getting full *and* the tape offload had stalled… As you can imagine this scenario is not pretty, so checking you Log storage groups is probably a good idea to guarantee you do not hit this problem!

That’s enough about UTS for this month. If IBM bring out another TLA for a TLA I will scream!


Roy Boxwell