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September 14, 2010

Access Path Stability and Skip Migration

I've been asked about the impact of migrating directly from DB2 8 to DB2 10. My standard response is if you're on V8 and plan to upgrade within a year, just go to DB2 9 rather than wait for V10. Julian Stuhler makes a detailed case for this approach here.

I recently traveled to IDUG Australia where I saw IBMer Terry Purcell's presentation on access path stability. No one knows the DB2 Optimizer like Terry does, and I always enjoy listening to and learning from him. His presentation was focused on V9 but also offered a look at what's ahead in V10. Terry threw out a word of caution for those who are thinking of moving from V8 to V10. IBM introduced access path stability in DB2 9 through APAR PK52522. The main purpose of this feature is to make it easier to migrate to new DB2 releases, in light of the fact that rebinding plans and packages is becoming a requirement rather than an option.

Terry said that skipping from V8 to V10 means you won't be able to use the access path stability feature to address any access path changes that negatively impact your system. However, access path stability isn't available for V8-to-V9 migrations, either. So why shouldn't you skip? Because V9 includes fixes that iron out many of the access path issues found in V8. So taking the one-step-at-a-time approach means you're far less likely to encouter problematic access path changes. And then, once you eventually migrate to V10, you can take advantage of REBIND with access path stability, which remedies negative access path changes by providing the capability to fall back to a previous access path.

To learn more about this, read Terry's thoughts here.