Post by: Haakon Roberts, DB2 for z/OS Development
Date: JUL 30, 2017 02:30 AM
Actual Article: PBR RPN explained
REORG with REBALANCEkeyword. But if some customers rely on partitioning scheme cant go with this approach.
The solution to these issues is two-fold.
First of all, DB2 has separated the partition number from the page number. This means that now RIDs are 7 bytes instead of 5: A 2-byte partition number, a 4-byte page number and a 1-byte IDMAP value (as before). Since the page number no longer contains the partition number, the page number is relative to the start of a given partition. Hence this enhancement is called “Relative Page Numbering”, i.e. PBR RPN. The partition number doesn’t need to be stored in each page, so one can no longer look at a data page and know which partition it belongs to. Note that this option applies to PBR table spaces only, not PBG or classic partitioned.
This means that now DB2 has broken the complex relationship between number of partitions, page size and DSSIZE. As a result, DB2 introduces a simple rule that individual partitions can now be up to 1Tb in size, regardless of number of partitions page size. Multiplied by 4096, this means that the maximum size of a PBR RPN table is 4Pb, and with a 4Kb page size and up to 255 rows per page, it equates to roughly 280 trillion rows.
The second piece of the PBR RPN solution is to start to drive some attributes from table space level down to partition level. In DB2 12 the primary focus is on DSSIZE. DSSIZE is now stored in SYSTABLEPART in addition to SYSTABLESPACE. An ALTER to increase DSSIZE for a PBR RPN table space is now possible for a single partition. Not only that, it is an immediate ALTER not even requiring a REORG to materialize. This represents a massive availability and usability improvement for PBR table spaces.
If you have LOB or XML columns in a table that is in a PBR RPN table space, then the XML table space will automatically be PBR RPN too and benefit from the same attributes. LOB table spaces are unaffected by PBR RPN.
Similarly, partitioned indexes (PI and DPSI) on PBR RPN table spaces now support DSSIZE on CREATE INDEX and ALTER INDEX, allowing you to manage index partition sizes independently of table space size.
PAGESET_PAGENUM. The options are
CREATE TABLESPACEhas also been enhanced to support a PAGENUM attribute where the options are
RELATIVE. The CREATE TABLESPACE option, if specified, overrides the zparm.
PAGENUM RELATIVEparameter. Tablespace will be placed in AREOR state and it requires a REORG of the entire tablespace.