Wednesday, October 14, 2020

Db2 12 for z/OS Function Level 508

This month, October 2020, IBM introduced the latest new function level, FL508, for Db2 12 for z/OS. This is the second new function level this year (the first came out in June and you can learn more about it here).

For those who don't know, the
Function Level process was designed by IBM for releasing new Db2 functionality using Continuous Delivery (CD) in short, quick bursts, instead of waiting for new versions (or releases). 

With FL508, IBM adds support for moving tables from multi-table table spaces, both simple and segmented, to partition-by-growth (PBG) universal table spaces (UTS). For an overview of UTS capabilities and types, check out this blog post I made earlier this year: Know Your Db2 Universal Table Spaces.

Multi-table table spaces are deprecated functionality, which means that even though they are still supported, they are on their way out. So it makes sense for IBM to give us a better way to convert them to PBG UTS without having to experience an outage. And that is just what FL508 delivers.

This is accomplished in FL508 by enhancements to the ALTER TABLESPACE statement. A new option, MOVE TABLE, is delivered which, as you might expect from its name, can be used to move a table from its current table space to a target table space. 

If, as you would expect in most cases, the source table space data sets are already created, the changes made by MOVE TABLE are pending changes and a REORG must be run on the source table space (the current one you are moving from) to materialize the change. Of course, this is an online REORG, so no outage is required.

The target table space must already exist as a PBG UTS in the same database as the current, source multi-table table space. Furthermore, the PBG UTS must be defined with MAXPARTITIONS 1, DEFINE NO, and [NOT] LOGGED and CCSID values that are the same as the current, existing table space. You can move only one table per ALTER TABLESPACE statement, meaning that each table in a multi-table table space must be moved with a separate ALTER TABLESPACE execution. However, because the changes are pending, you can issue multiple ALTER TABLESPACE statements, one for each table in the multi-table table space, and wait until they have all completed successfully before materializing all of the changes with a single REORG run. 

It seems simple, and the functionality is nice, but don't just go willy-nilly into things moving tables all over the place once you get this capability in FL508. IBM has documented the things to take care of before you begin to move tables using ALTER TABLESPACE. Check out the IBM recommendations here

It is also worth mentioning that you still need to keep in mind the impact that moving all tables from multi-table table spaces into their own table space will have on the system. By that I mean, you have to consider the potential impact on things like the number of open data sets (DSMAX ZPARM), DBD size, EDM pool size, and management issues (number of utility jobs, for example).

But it is nice that we now have a reasonable approach for moving tables out of deprecated multi-table table spaces so we can begin the process of moving them before they are no longer supported. A lot of shops "out there" have been waiting for something like this and it is likely to cause FL508 to be adopted quickly.

Let me know what you think by commenting below...


Julia Carter said...

Great article, thanks Craig. It’s interesting to understand how this long-awaited feature will actually work. I wonder if it’s a little too late for some people who were perhaps rushing to manually convert their multi table tablespaces prior to FL504? Either way, thank you for sharing!

Craig S. Mullins said...

You have a point there, Julia. I know of some shops that have converted manually already - but for those who haven't, and there are plenty of them, this new capability will save a lot of effort!