A Lot of Extraneous Data Sets?

In a recent blog post here I talked about a quick and dirty method of converting your partitioned table spaces from index-controlled to table-controlled. If you haven't read that post, take a moment to click over and read it here: Easily Convert to Table-Controlled Partitioning.

The reason I bring this up today is that I received an interesting e-mail from a long-time friend and DB2 DBA who read the post and had some information to share with me. He told me about how his organization used one of my tips to drop unused indexes as part of this process.

He told me that during the conversion process they dropped a lot of the clustering indexes because they weren't being used for access paths or for uniqueness. And they were able to release an "astonishing 4,100 data sets" by doing so!

Now I am not suggesting that every shop will be able to experience a similar savings, but if you have indexes that have no purpose other than enforcing index-controlled partitioning, it is time to bite the bullet and drop those indexes as you convert to table-controlled-partitioning (and then on to Universal table spaces).

And when you convert, please drop a note here on the blog to let us know how your conversion efforts went!

Easily Convert to Table-Controlled Partitioning

Up through DB2 V8 for z/OS, the only way to control partitioning of DB2 table spaces was by using a clustering index that specified the range of key values for each partition. With V8, though, DB2 adds the ability to specify the partitioning criteria in the CREATE TABLE specification. This is known as table-controlled partitioning and it is the preferred method for creating (non-Universal) partitioned table spaces. With table-controlled partitioning you can cluster on a different column (or set of columns) than you are partitioning on. Furthermore, you can make changes such as dropping a partitioning index or creating a table in a partitioned table space without defining any indexes at all.

But given the long history of DB2, many existing partitioned table spaces are index-controlled. 

Fortunately, there is a quick-and-dirty technique that you can use to easily convert from index-controlled to table-based partitioning. Simply follow these steps:

• Identify the index-controlled partitioned table space you wish to convert

• Convert the clustering index on the table to NOT CLUSTER using ALTER INDEX. (Alternately, you could drop the clustering index, but I wouldn’t recommend that unless you no longer need that index at all.)

• Convert the index back to CLUSTER, again using ALTER INDEX

Voila! DB2 will have converted your table space to table-controlled partitioning.

Note: DB2 will also convert from index-controlled to table-controlled partitioning if you use ALTER TABLE to add a new partition, change a partition boundary, or rotate a partition to last on an index-controlled partitioned table space. But these are more intrusive methods than simply altering the index from clustering to non-clustering and back again.