Monday, March 20, 2017

The DB2 12 for z/OS Blog Series – Part 7: Relative Page Number Table Spaces

One of the most significant new features for supporting big data in a DB2 12 environment is relative page numbering (or RPN) for range-partitioned table spaces. You can either create a new RPN range-partitioned table space, or an existing range-partitioned table space can be changed to RPN via an ALTER TABLESPACE with PAGENUM RELATIVE, followed by an online REORG of the entire table space.

But why would you want RPN table spaces instead of the already-existing table spaces types in DB2? The simple answer is the ability to grow the amount of data you store. RPN table spaces enable you to store large amounts of data. The DSSIZE can grow up to 1 TB for a partition. And the maximum table size increases to 4 PB with up to 256 trillion rows per table. That is a lot of data that can be stored! Think about it this way: if you were to insert 1000 rows per second it would take more than 8000 years to fill the table to capacity!

With RPN table spaces you get the ability to create larger partition sizes. The maximum partition size is now 1 TB (it used to be 256 GB). So if you are reaching the capacity size of existing table space options, RPN table spaces will allow you to store a LOT more data. Of course, this requires an expanded RID, which increases from 5 bytes to 7 bytes. So that will impact the DDL for the mapping table for your online REORG utilities.

But size is not the only issue. RPN table spaces improve availability, too. You can specify DSSIZE at the partition level for RPN table spaces. So each partition can have its own, different DSSIZE specification. Furthermore, the allowable DSSIZE value is no longer dependent on the page size and number of table space partitions. The DSSIZE change can be an immediate change (no online REORG required to take effect) as long as the change does not decrease the DSSIZE value.

As you move your DB2 subsystems to Version 12, consider migrating your larger range-partitioned table spaces to RPN to take advantage of these new capabilities.

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