One of the major headaches all DB2 users face when upgrading to a new release is the possibility of access path regression. In order to benefit from enhancements to the optimiser, plans and packages need to be rebound under the new release. The vast majority of the time, this will result in the same or better access path being selected, but just occasionally DB2 may select a worse one and performance suffers.
IBM has delivered some very useful new functionality in the maintenance stream for DB2 9 for z/OS to help to address this issue. PK52523 provides some new options for REBIND that allow the old version of an access path to be stored. If regression occurs, the previous access path can be quickly and easily re-established with another REBIND. This will be a significant benefit for V8 customers moving to V9, removing one of the biggest migration pain points. This functionality will be further enhanced in future releases of DB2.